Friday, February 13, 2026

Rebuilding World Economy Post-WWII Class 10 History | Bretton Woods IMF World Bank Notes + PYQ MCQ.

Rebuilding World Economy Post-WWII  

INTRODUCTION:

The Second World War (1939-1945) ended with victory for the Allies, but it left behind a devastated world economy. Two world wars within three decades had caused unprecedented death, destruction, and economic collapse. As the war ended, world leaders began planning how to rebuild the international economy and prevent future conflicts by creating new institutions and systems for economic cooperation. This section explores the post-war settlement at Bretton Woods, the creation of the IMF and World Bank, the fixed exchange rate system, the post-war economic boom, decolonization, and the rise of developing countries (G-77) demanding a fairer international economic order.

 

 


Post-War Settlement and the Bretton Woods Institutions

Why rebuild the international economy?

The Second World War ended in 1945, and economists and politicians across the world realized that for stable prosperity, full employment, and mass consumption, economic stability was essential. They wanted to prevent economic crises like the Great Depression and preserve peace.

The Bretton Woods Conference (1944)

Even before the war ended, the United Nations Monetary and Financial Conference was held in July 1944 at Bretton Woods in New Hampshire, USA. The Bretton Woods conference established the framework for post-war international economic order.

The main framework agreed upon at Bretton Woods included:

1.   National governments would be responsible for preserving economic stability and full employment.

2.   The International Monetary Fund (IMF) was set up to deal with external surpluses and deficits of member nations.

3.   The International Bank for Reconstruction and Development (World Bank) was created to finance post-war reconstruction.

The International Monetary Fund (IMF)

The IMF's main role was to maintain a system of fixed exchange rates between national currencies. Under the Bretton Woods system, national currencies were pegged (fixed) to the US dollar at a fixed exchange rate, and the dollar itself was anchored to gold at a fixed price of $35 per ounce of gold.

This system meant:

·       Exchange rates between currencies remained stable, making international trade predictable.

·       If a country faced a temporary balance of payments deficit (importing more than exporting), it could borrow foreign currencies from the IMF.

The World Bank

The World Bank was initially created to finance the reconstruction of war-torn Europe. Later, it shifted its focus to funding development projects in former colonies that became independent after the war.

Class 10 Science – Chapter 10: Light - Reflection and Refraction complete notes


The Early Post-War Years

Western industrial nations and Japan

The Bretton Woods system opened an era of unprecedented growth of trade and incomes for the Western industrial nations and Japan. Over the next 25 years (1950s-1970s), world trade grew annually at over 8%, and incomes at nearly 5%.

Why this growth happened

The growth was partly due to:

·       Technology improvements and enterprise that increased productivity.

·       The Bretton Woods system, which created stable exchange rates and allowed free movement of capital and goods between countries.

·       US dominance: The dollar became the world's principal currency, and the US military presence across the globe helped maintain political stability needed for economic growth.

Rise of multinational corporations (MNCs)

A major feature of the post-war economy was the spread of technology and enterprise across borders, often through multinational corporations (MNCs). US businesses began setting up factories and offices in Europe, and European and Japanese firms also spread globally.

Section 3: THE INTER-WAR ECONOMYChapter 3: The Making of a Global World


Decolonization and Independence

End of colonial empires

The Second World War weakened European colonial powers. After the war, most colonies in Asia and Africa became independent nations.

But independence didn't automatically bring prosperity. Most developing countries were still producers and exporters of raw materials (agricultural products and minerals) and importers of manufactured goods from the richer industrial countries of Europe, North America, and Japan.

Unequal terms of trade

For developing countries, the prices of raw materials (which they exported) were low and unstable, while the prices of manufactured goods (which they imported) were high. This created an unfair trading system that kept poor countries poor.

Class 10 Science – Chapter 9: Heredity and Evolution complete notes.


Demands for a New International Economic Order (NIEO)

Formation of the G-77

By the 1950s and 1960s, most developing countries organized themselves into a group called the Group of 77 (G-77) to demand better terms of trade and fairer international economic relations.

What did the G-77 demand?

The G-77 called for a New International Economic Order (NIEO), which would give developing countries:

·       Real control over their natural resources

·       More development assistance

·       Fairer prices for raw materials

·       Better access to markets in developed countries for their manufactured goods

The G-77 countries were united in their demand for a new system, but in reality they were very diverse. Some were rich in oil and minerals (like the OPEC countries), while others were desperately poor.

CLASS 10 HISTORY CH-3 | THE NINETEENTH CENTURY (1815-1914)


The OPEC Shock and the End of Bretton Woods

The oil crisis (1973)

In 1973, the Organization of Petroleum Exporting Countries (OPEC), led by Arab nations, decided to use oil as a political weapon and drastically increased the price of oil. Oil prices quadrupled (went up four times), causing a global economic crisis.

This oil shock had two major effects:

1.   It showed that developing countries (resource-rich ones like OPEC) could influence the global economy.

2.   It contributed to the collapse of the Bretton Woods system.

Collapse of Bretton Woods

The Bretton Woods system based on fixed exchange rates collapsed in the early 1970s. Several reasons contributed:

1.   The US dollar, which was the system's anchor, came under pressure because the US was spending heavily on the Vietnam War and welfare programs.

2.   Rising inflation in the US made it difficult to maintain the fixed price of $35 per ounce of gold.

3.   In 1971, the US abandoned the gold standard (meaning the dollar was no longer convertible to gold at a fixed rate).

4.   By 1973, the system of fixed exchange rates was replaced by a system of floating exchange rates, where currency values were determined by market forces.

Consequences of the collapse

The collapse of Bretton Woods and the oil crisis led to:

·       High inflation

·       Unemployment in industrial countries

·       Lower growth rates

·       Increased financial instability worldwide.

Class 10 Science – Chapter: How Do Organisms Reproduce?  


Globalization Since the 1970s-1980s

Rise of China and East Asia

From the mid-1970s, the international financial system became more integrated, but also more unstable. Developing countries were encouraged to borrow from Western banks and private lenders.

Meanwhile, China and several East Asian economies (like South Korea, Taiwan) began to grow rapidly by exporting manufactured goods to Western markets. By the 1980s-1990s, these countries became new economic powers.

Shift in global economic power

The decades after the collapse of Bretton Woods saw:

·       The rise of China as the "world's factory"

·       MNCs relocating production to low-wage countries

·       Growing inequality: some developing countries became rich, while many remained poor


Quick Revision Table

 

Topic

Key Points for Exams

Bretton Woods (1944)

Conference to rebuild post-WWII economy; created IMF & World Bank.

IMF

Maintains fixed exchange rates; provides short-term loans to countries with balance of payments problems.

World Bank

Finances post-war reconstruction and development projects in former colonies.

Fixed exchange rates

Currencies pegged to US dollar; dollar pegged to gold at $35/ounce.

Post-war growth

1950s-70s: world trade grew 8% annually; driven by technology, Bretton Woods system, US dominance, MNCs.

Decolonization

Most Asian/African colonies became independent after WWII; remained exporters of raw materials.

G-77

Group of developing countries demanding New International Economic Order (NIEO) for fairer trade.

1973 Oil crisis

OPEC raised oil prices 4x; global economic crisis; showed power of resource-rich developing countries.

End of Bretton Woods

System collapsed early 1970s; US abandoned gold standard (1971); shift to floating exchange rates.

 
THE PRE-MODERN WORLD (Before 1800s)Chapter 3: The Making of a Global World


MCQs PYQ

 

1.   The Bretton Woods Conference was held in:
A. 1939
B. 1944
C. 1950
D. 1971
Answer: B

2.   The IMF was created to:
A. Fight wars
B. Maintain fixed exchange rates and provide short-term loans
C. Stop migration
D. Control trade in oil
Answer: B

3.   Under the Bretton Woods system, the US dollar was pegged to gold at:
A. $10 per ounce
B. $25 per ounce
C. $35 per ounce
D. $50 per ounce
Answer: C

4.   The World Bank was initially created to:
A. Finance wars
B. Finance post-war reconstruction
C. Stop inflation
D. Control currencies
Answer: B

5.   The G-77 is a group of:
A. Industrial nations
B. Developing countries
C. Oil-exporting countries only
D. European nations
Answer: B

6.   The New International Economic Order (NIEO) was demanded by:
A. USA
B. Europe
C. G-77 developing countries
D. Japan
Answer: C

7.   The 1973 oil crisis was caused by:
A. Natural disasters
B. OPEC raising oil prices
C. World War II
D. Collapse of banks
Answer: B

8.   The Bretton Woods system collapsed in:
A. 1950s
B. Early 1970s
C. 1980s
D. 1990s
Answer: B

9.   After Bretton Woods collapsed, the world shifted to:
A. Fixed exchange rates
B. Floating exchange rates
C. Gold standard
D. Barter system
Answer: B

10.                 Which country became known as the "world's factory" from the 1980s-1990s?
A. USA
B. Britain
C. China
D. Germany
Answer: C



Short Answer Questions (PYQ)

 

Q1. What were the main features of the Bretton Woods system?

Answer: The Bretton Woods system (1944) created the IMF to maintain fixed exchange rates between currencies (pegged to the US dollar, which was anchored to gold at $35/ounce). The World Bank was created to finance post-war reconstruction and later development projects. National governments were made responsible for maintaining economic stability and full employment.

Q2. What was the role of the IMF?

Answer: The IMF was established to deal with external surpluses and deficits of member nations by maintaining a system of fixed exchange rates. It provided short-term loans to countries facing temporary balance of payments problems (when imports exceeded exports). This helped stabilize international trade and currency values.

Q3. What was the G-77? What did it demand?

Answer: The G-77 was a group of developing countries formed in the 1950s-60s to demand a New International Economic Order (NIEO). They wanted real control over natural resources, fairer prices for raw materials, better terms of trade, and access to developed country markets for their manufactured goods.

Q4. Why did the Bretton Woods system collapse?

Answer: The system collapsed in the early 1970s because the US dollar came under pressure due to heavy spending on the Vietnam War and welfare programs, causing inflation. In 1971, the US abandoned the gold standard (dollar no longer convertible to gold at $35/ounce). By 1973, fixed exchange rates were replaced by floating exchange rates determined by market forces.

Q5. What was the 1973 oil crisis?

Answer: In 1973, OPEC (Organization of Petroleum Exporting Countries) drastically raised oil prices, which quadrupled (went up four times). This caused a global economic crisis with high inflation and unemployment in industrial countries. It showed that resource-rich developing countries could influence the global economy.


Long Answer Questions (PYQ)

 

Q1. Explain the Bretton Woods system and its institutions.

Answer: The Bretton Woods Conference (July 1944) established the framework for the post-WWII international economic order to preserve economic stability, full employment, and prevent another Great Depression. It created two key institutions: the International Monetary Fund (IMF) to maintain fixed exchange rates and provide short-term loans to countries with balance of payments deficits, and the International Bank for Reconstruction and Development (World Bank) to finance post-war reconstruction and later development projects in former colonies. Under this system, national currencies were pegged to the US dollar at fixed rates, and the dollar was anchored to gold at $35 per ounce, ensuring stable and predictable exchange rates. National governments were made responsible for maintaining economic stability. This system opened an era of unprecedented growth in trade and incomes for Western industrial nations and Japan from the 1950s to 1970s.

Q2. Why did developing countries demand a New International Economic Order?

Answer: After gaining independence following WWII, most developing countries remained exporters of raw materials (agricultural products and minerals) and importers of manufactured goods from richer nations. The prices of raw materials they exported were low and unstable, while the prices of manufactured goods they imported were high, creating unfair terms of trade. By the 1950s-60s, these countries organized themselves into the Group of 77 (G-77) to collectively demand a New International Economic Order (NIEO). They wanted real control over their natural resources, more development assistance, fairer prices for raw materials, and better access to developed country markets for their manufactured goods. Though united in demands, G-77 countries were diverse—some were resource-rich (like OPEC nations) while others were desperately poor.

Q3. Explain the causes and consequences of the collapse of the Bretton Woods system.

Answer: The Bretton Woods system of fixed exchange rates collapsed in the early 1970s due to multiple pressures. The US dollar, which anchored the system, came under strain because the US was spending heavily on the Vietnam War and domestic welfare programs, leading to rising inflation. This made it difficult to maintain the fixed gold price of $35 per ounce. In 1971, the US abandoned the gold standard, meaning the dollar was no longer convertible to gold at a fixed rate, and by 1973 the system of fixed exchange rates was replaced by floating exchange rates determined by market forces. The collapse, combined with the 1973 OPEC oil crisis (which quadrupled oil prices), led to high inflation, unemployment in industrial countries, lower growth rates, and increased financial instability worldwide.


Conclusion


The post-WWII period saw the creation of new international institutions (IMF and World Bank) at Bretton Woods to rebuild the global economy and prevent future depressions. The system of fixed exchange rates brought unprecedented growth to Western nations and Japan in the 1950s-70s, but developing countries remained trapped in unfair trade patterns as raw material exporters. The G-77 demanded a fairer New International Economic Order, while the 1973 oil crisis and the collapse of Bretton Woods in the early 1970s ushered in a new era of floating exchange rates, financial instability, and the rise of new economic powers like China. For board exams, focus on Bretton Woods institutions, fixed vs. floating exchange rates, G-77 demands, and reasons for the system's collapse—these are frequently tested.


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Wednesday, February 11, 2026

Class 10 Science Chapter: Light – Reflection and Refraction (Complete Notes)

Light – Reflection and Refraction

INTRODUCTION:

Light – Reflection and Refraction is one of those Class 10 Physics chapters where understanding sign conventions, ray diagram rules, and three formulas (mirror formula, lens formula, magnification) unlocks almost every question. The chapter divides cleanly into two parts: reflection (how light bounces off mirrors - spherical mirrors, ray diagrams, mirror formula) and refraction (how light bends when passing through different media - lenses, refractive index, lens formula). Board exams consistently test ray diagrams (3 marks), numerical problems using formulas (3-5 marks), and "differentiate between" questions (concave vs convex mirrors/lenses). Master the New Cartesian Sign Convention, practice 10-15 numericals, and draw ray diagrams for all six standard object positions—this strategy alone secures 10+ marks in Board 2026.

 

Class 10 Science Chapter: Light – Reflection and Refraction (Complete Notes)



REFLECTION OF LIGHT

Reflection of light

Reflection is the phenomenon of bouncing back of light into the same medium when it strikes a smooth surface.

Key terms:

·       Incident ray: Light ray falling on the surface

·       Reflected ray: Light ray bouncing back after reflection

·       Normal: Perpendicular line drawn at the point of incidence

·       Angle of incidence (i): Angle between incident ray and normal

·       Angle of reflection (r): Angle between reflected ray and normal

Laws of reflection

1.   The incident ray, reflected ray, and normal all lie in the same plane

Angle of incidence = Angle of reflection (i = r)

Section 3: THE INTER-WAR ECONOMY Chapter 3: The Making of a Global World  


Spherical mirrors

Spherical mirror: Mirror whose reflecting surface is part of a hollow sphere.

Types

Mirror type

Reflecting surface

Effect on light

Also called

Concave mirror

Inner curved surface (caved in)

Converges parallel rays

Converging mirror

Convex mirror

Outer bulging surface

Diverges parallel rays

Diverging mirror

 

Important terms for spherical mirrors

Term

Definition

Symbol

Pole (P)

Center point of the mirror

P

Center of curvature (C)

Center of the sphere of which mirror is part

C

Radius of curvature (R)

Radius of the sphere of which mirror is part

R

Principal axis

Line joining pole and center of curvature

Principal focus (F)

Point on principal axis where parallel rays converge (concave) or appear to diverge from (convex)

F

Focal length (f)

Distance between pole and focus

f

Aperture

Diameter of the reflecting surface of mirror

Relationship: Focal length = Half of radius of curvature
f=R/2

Ray diagram rules for spherical mirrors

For both concave and convex mirrors:

1.   A ray parallel to principal axis, after reflection, passes through focus F (concave) or appears to come from F (convex)

2.   A ray passing through focus F (concave) or directed towards F (convex), after reflection, becomes parallel to principal axis

3.   A ray passing through center of curvature C, reflects back along the same path

4.   A ray striking the pole makes equal angles with principal axis (incident and reflected)

Class 10 Science – Chapter 9: Heredity and Evolution complete notes. 


Image formation by concave mirror

 

Object position

Image position

Image nature

Image size

Ray diagram use

At infinity

At focus F

Real, inverted

Highly diminished (point)

Beyond C

Between F and C

Real, inverted

Diminished

At C

At C

Real, inverted

Same size

Between C and F

Beyond C

Real, inverted

Magnified (enlarged)

At F

At infinity

Real, inverted

Highly magnified

Searchlights, headlights

Between F and P

Behind the mirror

Virtual, erect

Magnified

Shaving mirror, makeup mirror, dentist mirror

 

Image formation by convex mirror

Object position

Image position

Image nature

Image size

At infinity

At focus F (behind mirror)

Virtual, erect

Highly diminished (point)

Anywhere between infinity and pole

Between P and F (behind mirror)

Virtual, erect

Diminished

 

Uses of convex mirror: Rear-view mirrors in vehicles (gives wide field of view), shop security mirrors.

 

CLASS 10 HISTORY CH-3 | THE NINETEENTH CENTURY (1815-1914)  


Sign convention for mirrors (New Cartesian Sign Convention)

Measurement

Sign

Explanation

Object distance (u)

Always negative

Object always in front of mirror

Image distance (v)

Negative if real (in front)

Real images form in front

Image distance (v)

Positive if virtual (behind)

Virtual images form behind mirror

Focal length (f)

Negative for concave

Focus in front

Focal length (f)

Positive for convex

Focus behind

Height above principal axis

Positive

Upward direction positive

Height below principal axis

Negative

Downward direction negative

 

Mirror formula

1/f=1/v+1/u

Where:

·       f = focal length of mirror

·       v = image distance from pole

·       u = object distance from pole

Remember: Use proper signs according to sign convention!

Magnification for mirrors

Linear magnification (m): Ratio of height of image to height of object

m=h′/h=−v/u

Where:

·       h = height of object

·       h' = height of image

·       v = image distance

·       u = object distance

Interpretation:

·       If m is negative Image is real and inverted

·       If m is positive Image is virtual and erect

·       If |m| > 1 Image is magnified (enlarged)

·       If |m| < 1 Image is diminished (smaller)

·       If |m| = 1 Image is same size as object

Class 10 Science – Chapter: How Do Organisms Reproduce?  


REFRACTION OF LIGHT

 

Refraction of light

Refraction: The bending of light when it passes from one transparent medium to another.

Why does refraction occur? Light travels at different speeds in different media.

Key terms:

·       Optically rarer medium: Medium where light travels faster (e.g., air)

·       Optically denser medium: Medium where light travels slower (e.g., glass, water)

·       Angle of incidence (i): Angle between incident ray and normal

·       Angle of refraction (r): Angle between refracted ray and normal

Bending behavior:

·       Light bends towards normal when entering denser medium (air glass)

·       Light bends away from normal when entering rarer medium (glass air)

Laws of refraction

First law: Incident ray, refracted ray, and normal all lie in the same plane

Second law (Snell's Law): The ratio of sine of angle of incidence to sine of angle of refraction is constant

Sin i/sin r=constant=μ

Where μ (mu) is the refractive index.

 

THE PRE-MODERN WORLD (Before 1800s) Chapter 3: The Making of a Global World 


Refractive index

Refractive index represents the extent of bending of light in a medium.

1. Absolute refractive index: Refractive index of medium with respect to air/vacuum.

μm=c/vm

Where:

·       c = speed of light in air/vacuum (3 × 10⁸ m/s)

·       v_m = speed of light in medium

2. Relative refractive index: Refractive index of one medium with respect to another

μ21=v1/v2=μ2/μ1

Refractive indices of common substances:

·       Air: 1.0003 (≈ 1)

·       Water: 1.33

·       Glass: 1.5

·       Diamond: 2.42


Spherical lenses

Lens: Transparent refracting medium bounded by two surfaces, at least one of which is curved.

Types

Lens type

Shape

Effect on light

Also called

Focal length sign

Convex lens

Thicker at center, thinner at edges

Converges parallel rays

Converging lens

Positive (+)

Concave lens

Thinner at center, thicker at edges

Diverges parallel rays

Diverging lens

Negative (−)

 

Important terms for lenses

Term

Definition

Optical center (C)

Central point of lens; rays passing through it go undeviated

Principal axis

Line joining the two centers of curvature

Principal focus (F)

Point where parallel rays converge (convex) or appear to diverge from (concave) after refraction

Focal length (f)

Distance between optical center and principal focus

 

Ray diagram rules for lenses

For both convex and concave lenses:

1.   A ray parallel to principal axis, after refraction, passes through focus F (convex) or appears to come from F (concave)

2.   A ray passing through optical center C goes straight without bending

3.   A ray passing through focus F (convex) or directed towards F (concave), after refraction, becomes parallel to principal axis.

Class 10 Science – Chapter 6: Control and Coordination 


Image formation by convex lens

Object position

Image position

Image nature

Image size

Use

At infinity

At focus F

Real, inverted

Highly diminished

Beyond 2F

Between F and 2F

Real, inverted

Diminished

Camera

At 2F

At 2F

Real, inverted

Same size

Between F and 2F

Beyond 2F

Real, inverted

Magnified

Projector

At F

At infinity

Real, inverted

Highly magnified

Between F and optical center

Same side as object

Virtual, erect

Magnified

Magnifying glass

 

Image formation by concave lens

Object position

Image position

Image nature

Image size

At infinity

At focus F

Virtual, erect

Highly diminished

Anywhere between infinity and lens

Between F and optical center

Virtual, erect

Diminished

 

Sign convention for lenses (New Cartesian Sign Convention)

Origin: All distances measured from optical center (C) of lens

Measurement

Sign

Explanation

Object distance (u)

Always negative

Object always on left side (in front)

Image distance (v)

Positive if real (right side)

Real images on opposite side

Image distance (v)

Negative if virtual (same side as object)

Virtual images on same side

Focal length (f)

Positive for convex lens

Converging lens

Focal length (f)

Negative for concave lens

Diverging lens

Height above principal axis

Positive

Upward positive

Height below principal axis

Negative

Downward negative

 


Lens formula

1/f=1/v−1/u

Where:

·       f = focal length of lens

·       v = image distance from optical center

·       u = object distance from optical center

Note: Different from mirror formula! Minus sign instead of plus.

 

Magnification for lenses

m=h′/h=v/u

Where:

·       h = height of object

·       h' = height of image

·       v = image distance

·       u = object distance

Interpretation:

·       If m is negative Image is real and inverted

·       If m is positive Image is virtual and erect

·       If |m| > 1 Magnified

·       If |m| < 1 Diminished

 

Power of lens

Power (P): Ability of a lens to converge or diverge light rays.

P=1/f (in meters)

Unit: Dioptre (D)

Sign:

·       Convex lens: Positive power

·       Concave lens: Negative power

Example: If f = 50 cm = 0.5 m, then P = 1/0.5 = +2 D (convex lens).

THE SENSE OF COLLECTIVE BELONGING (Chapter 2: Nationalism in India — NCERT) 


Mirrors vs Lenses comparison

Feature

Concave mirror

Convex mirror

Convex lens

Concave lens

Nature

Converging

Diverging

Converging

Diverging

Focal length sign

Negative (−)

Positive (+)

Positive (+)

Negative (−)

Can form real image

Yes

No

Yes

No

Can form virtual image

Yes

Yes

Yes

Yes

Can form magnified image

Yes

No

Yes

No

Formula

1/f = 1/v + 1/u

1/f = 1/v + 1/u

1/f = 1/v − 1/u

1/f = 1/v − 1/u

Power

Not defined

Not defined

Positive

Negative

 Chapter 6 Life Processes complete notes


MCQs PYQ

 

1. The angle of incidence equals the angle of reflection. This is:
(a) First law of reflection
(b) Second law of reflection
(c) Law of refraction
(d) Snell's law
Answer: (b) Second law of reflection. (CBSE 2020)

 

2. The focal length of a concave mirror is 15 cm. Its radius of curvature is:
(a) 7.5 cm
(b) 15 cm
(c) 30 cm
(d) 45 cm
Answer: (c) R = 2f = 2 × 15 = 30 cm. (CBSE 2024)

 

3. A convex mirror is used as rear-view mirror because:
(a) It forms magnified image
(b) It gives wider field of view
(c) It forms real image
(d) It has long focal length
Answer: (b) Wider field of view. (CBSE 2023)

 

4. The SI unit of power of a lens is:
(a) Watt
(b) Dioptre
(c) Meter
(d) Candela
Answer: (b) Dioptre (D). (CBSE 2020)

 

5. A concave lens always forms an image which is:
(a) Real and magnified
(b) Real and diminished
(c) Virtual and diminished
(d) Virtual and magnified
Answer: (c) Virtual, erect, and diminished. (CBSE 2024)

 

6. The magnification produced by a plane mirror is:
(a) Zero
(b) +1
(c) −1
(d) Infinity
Answer: (b) +1 (same size, virtual, erect). (CBSE 2020)

 

7. If the image formed by a mirror is virtual, erect, and magnified, the mirror is:
(a) Concave
(b) Convex
(c) Plane
(d) Either concave or convex
Answer: (a) Concave mirror (object between F and P). (CBSE 2023)

 

8. Light travels fastest in:
(a) Glass
(b) Water
(c) Diamond
(d) Vacuum
Answer: (d) Vacuum (or air). (CBSE 2020)

 

9. The power of a lens having focal length 50 cm is:
(a) +0.5 D
(b) −0.5 D
(c) +2 D
(d) −2 D
Answer: (c) P = 1/f = 1/0.5 = +2 D (convex lens). (CBSE 2024)

 

10. A ray of light bends towards normal when it enters from air to glass because:
(a) Glass is denser than air
(b) Air is denser than glass
(c) Speed of light increases
(d) Refraction does not occur
Answer: (a) Glass is optically denser than air. (CBSE 2020).

 

Class 10 Students (Board Exam 2026)! Chapter 4 Carbon and its Compounds 



Short Answer Questions (PYQ)

 

Q1. State laws of reflection.


Answer:
(1) Incident ray, reflected ray, and normal lie in the same plane. (2) Angle of incidence = Angle of reflection (i = r). (CBSE 2020)

 

Q2. Define the principal focus of a concave mirror.

Answer: Principal focus is the point on the principal axis where all light rays parallel to the principal axis converge after reflection from the concave mirror. (CBSE 2023)

 

Q3. Distinguish between real and virtual images.

Answer: Real image: formed by actual intersection of light rays, can be obtained on screen, always inverted. Virtual image: formed by apparent intersection of light rays, cannot be obtained on screen, always erect. (CBSE 2020)

 

Q4. What is meant by power of a lens? Write its SI unit.

Answer:
Power of a lens is its ability to converge (convex) or diverge (concave) light rays. It is reciprocal of focal length in meters. SI unit: Dioptre (D). Formula: P = 1/f (in meters). (CBSE 2024)

 

Q5. Why does a ray of light bend when it travels from one medium to another?

Answer: Light bends (refracts) because its speed changes when it travels from one medium to another. Speed depends on optical density of the medium. Light bends towards normal when entering denser medium and away from normal when entering rarer medium. (CBSE 2020)


Long Answer Questions (PYQ)

 

Q1. An object 5 cm high is placed at a distance of 30 cm from a concave mirror of focal length 20 cm. Find the position, nature, and size of the image.

Answer:
Given: h = 5 cm, u = −30 cm, f = −20 cm
Using mirror formula: 1/f = 1/v + 1/u
1/(−20) = 1/v + 1/(−30)
1/v = 1/(−20) + 1/30 = (−3 + 2)/60 = −1/60
v = −60 cm (negative means real image, in front of mirror)

Magnification: m = −v/u = −(−60)/(−30) = −2
Image height: h' = m × h = −2 × 5 = −10 cm (negative means inverted)

Answer: Image is at 60 cm in front of mirror, real, inverted, magnified (10 cm high). (CBSE 2020)

 

Q2. A convex lens has focal length 15 cm. An object is placed at 30 cm from the lens. Calculate image distance and magnification.

Answer:
Given: u = −30 cm, f = +15 cm
Using lens formula: 1/f = 1/v − 1/u
1/15 = 1/v − 1/(−30)
1/15 = 1/v + 1/30
1/v = 1/15 − 1/30 = (2 − 1)/30 = 1/30
v = +30 cm (positive means real image on opposite side)

Magnification: m = v/u = 30/(−30) = −1

Answer: Image distance = 30 cm (real), magnification = −1 (same size, inverted). (CBSE 2024)

 

Q3. Draw ray diagram for convex lens when object is placed between F and 2F. State the nature, position, and size of image formed.
Answer: (Ray diagram description): Draw three rays: (1) Parallel to principal axis, refracts through F
on other side, (2) Through optical center, goes straight, (3) Through F, emerges parallel to principal axis. All three rays meet beyond 2F.
Image: Real, inverted, magnified, beyond 2F
(used in projectors). (CBSE 2020)

Q4. A concave lens has power −2 D. An object is placed at 50 cm from the lens. Find image distance.

Answer:
Given: P = −2 D, so f = 1/P = 1/(−2) = −0.5 m = −50 cm
u = −50 cm
Using lens formula: 1/f = 1/v − 1/u
1/(−50) = 1/v − 1/(−50)
1/(−50) = 1/v + 1/50
1/v = 1/(−50) − 1/50 = (−1 − 1)/50 = −2/50 = −1/25
v = −25 cm (negative means virtual image on same side)

Answer: Image at 25 cm on same side as object, virtual, erect, diminished. (CBSE 2023)

 

Q5. Explain with diagram how concave mirror is used in solar furnace.

Answer: Large concave mirror with sun at infinity focuses all parallel sun rays at its focus point. This concentrates enormous amount of solar energy at the focus, producing very high temperature. The object to be heated is kept at this focus point. This is the principle of solar furnace. (Diagram: Draw concave mirror with parallel rays from sun converging at focus). (CBSE 2020)


Conclusion


Light – Reflection and Refraction becomes manageable when you organize it into clear sections: (1) Reflection (laws, spherical mirrors, ray diagrams for 6 object positions with concave mirror and 1 with convex mirror, mirror formula, magnification), and (2) Refraction (laws, refractive index, spherical lenses, ray diagrams for 6 object positions with convex lens and 1 with concave lens, lens formula, magnification, power of lens). The key strategy: memorize sign conventions first (u always negative, f negative for concave mirror/lens, f positive for convex mirror/lens, v sign depends on real/virtual), practice 15-20 numerical problems covering all formula variations, and draw ray diagrams for all standard positions until you can do them blindfolded. Remember that mirror formula uses + (1/f = 1/v + 1/u) while lens formula uses − (1/f = 1/v − 1/u)—this single difference causes most errors. This formula-based chapter rewards practice over theory and can easily secure 10-12 marks in Board 2026 with systematic preparation


Download Class 10 Science Notes PDF

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