I85PREP
⌘ K
Maharashtra SSC Science and Technology (MSBSHSE) study materials
Maharashtra SSC Science and Technology (MSBSHSE) study resources

Maharashtra SSC Science and Technology (MSBSHSE) practice questions

One question at a time. Build your Maharashtra SSC Science and Technology (MSBSHSE) understanding.

First 50 of 200 questions. Each one lists the choices, the correct answer, and an explanation. The checker at the top of this page saves progress in this browser when it is available.

Continue in the practice tool above to load more questions, 50 at a time.

Question 1Gravitation, Motion and Forces

According to Newton's law of gravitation, the gravitational force between two point masses kept at a fixed distance is directly proportional to which quantity?

  1. The product of the two masses Correct answer.
  2. The difference of the two masses
  3. The sum of the two masses
  4. The square of the distance between them

Explanation

Newton's law gives F = G m1 m2 / r². At a fixed separation r, the force varies directly as the product m1m2, while it varies inversely as the square of the distance. Sum and difference of masses do not appear in the law.

Question 2Gravitation, Motion and Forces

The SI unit of the universal gravitational constant G is:

  1. N m² kg
  2. N m² kg⁻² Correct answer.
  3. N m kg⁻¹
  4. N kg² m⁻²

Explanation

From F = G m1m2/r², we get G = Fr²/(m1m2). Substituting SI units gives N m² kg⁻². This unit follows because G has dimensions of force times length squared divided by mass squared.

Question 3Gravitation, Motion and Forces

A stone is dropped from rest near Earth's surface, and air resistance is neglected. Which statement describes its motion?

  1. It falls with a velocity that remains constant at 9.8 m/s.
  2. It falls with a constant acceleration of about 9.8 m/s². Correct answer.
  3. It falls with acceleration that decreases as it descends.
  4. It falls with acceleration that increases as it descends.

Explanation

Near Earth's surface, the acceleration due to gravity is approximately constant at 9.8 m/s² downward. The stone's velocity increases uniformly, not at a constant value. The acceleration does not steadily increase or decrease during the fall.

Question 4Gravitation, Motion and Forces

An object is taken from Earth to the Moon. Which quantity remains the same and which changes?

  1. Mass changes; weight remains the same.
  2. Both mass and weight change.
  3. Mass remains the same; weight changes. Correct answer.
  4. Both mass and weight remain the same.

Explanation

Mass is the amount of matter in an object and does not depend on location. Weight is the gravitational force mg, so it changes when the acceleration due to gravity changes. The Moon's surface gravity is about one-sixth of Earth's, so the object weighs less there.

Question 5Gravitation, Motion and Forces

Kepler's second law states that the line joining a planet to the Sun sweeps out equal areas in equal intervals of time. This law is a consequence of conservation of:

  1. Angular momentum Correct answer.
  2. Linear momentum
  3. Energy
  4. Mass

Explanation

The equal-area law is equivalent to the planet having constant angular momentum about the Sun. The gravitational force acts along the line joining the planet and the Sun, so its torque about the Sun is zero. With zero external torque, angular momentum is conserved.

Question 6Gravitation, Motion and Forces

A ball is thrown vertically upward with a velocity of 20 m/s. Taking g = 10 m/s² and neglecting air resistance, what is the maximum height reached?

  1. 5 m
  2. 20 m Correct answer.
  3. 40 m
  4. 10 m

Explanation

At the maximum height the final velocity is zero. Using v² = u² − 2gh gives 0 = (20)² − 2(10)h, so h = 400/20 = 20 m. The upward speed decreases uniformly until it becomes zero at the top.

Question 7Gravitation, Motion and Forces

A satellite moves in a circular orbit around Earth. The gravitational force on it provides the ____ required for circular motion, and this force points toward ____.

  1. centrifugal force; away from Earth's centre
  2. frictional force; opposite to velocity
  3. centripetal force; Earth's centre Correct answer.
  4. tangential force; along the velocity

Explanation

For circular motion, a centripetal force directed toward the centre of the circle is required. In a satellite orbit, Earth's gravitational attraction supplies this centripetal force. The force therefore points toward Earth's centre, not along the satellite's velocity.

Question 8Gravitation, Motion and Forces

Earth attracts an apple with a force F. According to Newton's third law, the apple attracts Earth with:

  1. a force much smaller than F because Earth is much more massive
  2. a force larger than F because the apple is accelerating
  3. no force, because the apple cannot exert gravity
  4. an equal force F in the opposite direction Correct answer.

Explanation

Newton's third law says that if Earth exerts a force F on the apple, the apple exerts an equal and opposite force F on Earth. These two forces form an action-reaction pair. Earth's much larger mass means its acceleration is extremely small, not that the force is smaller.

Question 9Gravitation, Motion and Forces

Ignoring air resistance and Earth's rotation, a projectile is fired from Earth's surface with a speed equal to escape velocity in a direction that does not immediately strike the ground. What is the result?

  1. It escapes Earth's gravity, because escape speed is independent of launch direction. Correct answer.
  2. It returns to Earth, because the required speed is 112 km/s.
  3. It cannot escape, because escape speed applies only to a vertical launch.
  4. It escapes only if it is launched exactly horizontally.

Explanation

Escape velocity is the minimum speed at the surface for the total mechanical energy to be zero or positive. This energy condition depends on the speed, not on the direction of launch, provided the projectile does not hit the ground or atmosphere. Thus any upward direction with the same speed can lead to escape.

Question 10Gravitation, Motion and Forces

At a height h above Earth's surface, where h is much smaller than Earth's radius R, the acceleration due to gravity is approximately g' = g(1 − 2h/R). At a depth d below the surface, g' = g(1 − d/R). Which comparison is correct for the same small numerical value h = d?

  1. g increases with height and decreases with depth.
  2. The decrease in g is the same at height h and depth d.
  3. The decrease in g at height h is half the decrease at depth d.
  4. The decrease in g at height h is twice the decrease at depth d. Correct answer.

Explanation

At height h, the fractional decrease in g is about 2h/R. At depth d, the fractional decrease is about d/R. For h = d, the decrease at height is therefore twice the decrease at the same numerical depth.

Question 11Gravitation, Motion and Forces

A passenger standing in a stationary bus tends to fall backward when the bus starts suddenly. Which property of the passenger explains this?

  1. Inertia of motion
  2. Inertia of rest Correct answer.
  3. Gravitational attraction
  4. Conservation of momentum

Explanation

The passenger is initially at rest and tends to remain at rest because of inertia of rest. When the bus starts, the lower part of the body moves with the bus while the upper part lags behind, so the passenger falls backward.

Question 12Gravitation, Motion and Forces

A body moves along a circular path with constant speed. At a given instant, the direction of its velocity is:

  1. Along the radius towards the centre
  2. Along the radius away from the centre
  3. Along the chord joining the body to the centre
  4. Along the tangent to the circle at that point Correct answer.

Explanation

Velocity at any instant is directed along the tangent to the circular path. In uniform circular motion the speed is constant, but the direction changes continuously, so the velocity changes.

Question 13Gravitation, Motion and Forces

A stone released from rest falls freely under gravity. The distances covered by it in the first, second and third seconds are in the ratio:

  1. 1 : 1 : 1
  2. 1 : 4 : 9
  3. 1 : 2 : 3
  4. 1 : 3 : 5 Correct answer.

Explanation

For a body falling from rest, the distance covered in the nth second is proportional to (2n − 1). Hence the distances in the first, second and third seconds are in the ratio 1 : 3 : 5.

Question 14Gravitation, Motion and Forces

If the distance between two point masses is doubled while their masses remain unchanged, the gravitational force between them becomes:

  1. F/4 Correct answer.
  2. F/2
  3. 4F
  4. 2F

Explanation

Newton's law of gravitation gives F = G m₁m₂/r², so the force is inversely proportional to the square of the distance. Doubling r makes the force one-fourth of its previous value.

Question 15Gravitation, Motion and Forces

A planet has twice the mass of Earth and twice the radius of Earth. If the acceleration due to gravity on Earth's surface is g, the acceleration due to gravity on the planet's surface is:

  1. g
  2. 2g
  3. g/2 Correct answer.
  4. 4g

Explanation

The acceleration due to gravity is g = GM/R². Substituting M′ = 2M and R′ = 2R gives g′ = G(2M)/(2R)² = (2/4)(GM/R²) = g/2.

Question 16Gravitation, Motion and Forces

Two satellites orbit Earth in circular orbits of radii r and 4r. The ratio of their periods T₁ : T₂ is:

  1. 1 : 4
  2. 1 : 16
  3. 1 : 2
  4. 1 : 8 Correct answer.

Explanation

Kepler's third law states that T² ∝ r³, so T ∝ r^(3/2). For radii in the ratio 1 : 4, the periods are in the ratio 1^(3/2) : 4^(3/2), which is 1 : 8.

Question 17Gravitation, Motion and Forces

A force of 20 N acts for 4 s on a 5 kg body initially at rest. The change in momentum of the body is:

  1. 20 kg m/s
  2. 80 kg m/s Correct answer.
  3. 4 kg m/s
  4. 40 kg m/s

Explanation

Impulse equals force multiplied by time, and impulse is equal to the change in momentum. Thus the change in momentum is 20 N × 4 s = 80 kg m/s.

Question 18Gravitation, Motion and Forces

An astronaut inside an orbiting space station feels weightless because:

  1. The astronaut and the station share the same free-fall acceleration Correct answer.
  2. Gravity is absent at the orbital height
  3. The station has moved beyond Earth's gravitational field
  4. The astronaut's mass becomes zero in orbit

Explanation

Inside an orbiting station, both the astronaut and the station are in free fall toward Earth with the same acceleration. The floor does not push the astronaut, so the normal reaction and apparent weight are zero.

Question 19Gravitation, Motion and Forces

A satellite in a circular orbit of radius 2R from Earth's centre has orbital speed v. Another satellite in a circular orbit of radius 8R from Earth's centre has orbital speed:

  1. v/2 Correct answer.
  2. 2v
  3. v/4
  4. v

Explanation

For a circular orbit, gravitational force provides the centripetal force, so GMm/r² = mv²/r and v = √(GM/r). Thus v ∝ 1/√r; when r becomes four times larger, v becomes half.

Question 20Gravitation, Motion and Forces

A person of mass 60 kg stands on a weighing scale in a lift that accelerates upward at 2 m/s². Taking g = 10 m/s², the reading of the scale is:

  1. 480 N
  2. 600 N
  3. 840 N
  4. 720 N Correct answer.

Explanation

In an upward-accelerating lift, the floor must provide the true weight plus the extra force for acceleration. The apparent weight is R = m(g + a) = 60(10 + 2) = 720 N.

Question 21Heat and Thermal Phenomena

At which temperature does water show its maximum density?

  1. 4 °C Correct answer.
  2. 0 °C
  3. 100 °C
  4. 10 °C

Explanation

Water contracts when heated from 0 °C to 4 °C and expands above 4 °C, so its volume is least and its density greatest at 4 °C. This anomalous expansion of water is the reason ice formed at 0 °C floats on the water below it.

Question 22Heat and Thermal Phenomena

The SI unit of specific heat capacity is

  1. J·kg/°C
  2. J/(kg·°C·m)
  3. J/(kg·°C) Correct answer.
  4. J/kg

Explanation

Specific heat capacity is the heat energy needed to raise the temperature of unit mass of a substance through one degree. Dividing heat energy (joule) by mass (kilogram) and by temperature rise (degree Celsius) gives the unit J/(kg·°C).

Question 23Heat and Thermal Phenomena

The heat of the Sun reaches the Earth through space mainly by

  1. convection
  2. conduction and convection together
  3. conduction
  4. radiation Correct answer.

Explanation

Radiation carries heat as electromagnetic waves and needs no material medium, which is why solar energy can cross the vacuum between the Sun and the Earth. Conduction and convection both require matter to transfer heat.

Question 24Heat and Thermal Phenomena

How much heat is needed to raise the temperature of 2 kg of water by 10 °C? (Specific heat capacity of water = 4200 J/(kg·°C))

  1. 168000 J
  2. 8400 J
  3. 42000 J
  4. 84000 J Correct answer.

Explanation

The heat required is Q = mcΔT. Substituting m = 2 kg, c = 4200 J/(kg·°C) and ΔT = 10 °C gives Q = 2 × 4200 × 10 = 84000 J. The large specific heat capacity of water is why warming it needs so much energy.

Question 25Heat and Thermal Phenomena

Water boils at 100 °C at normal atmospheric pressure. While boiling continues, the thermometer in the water keeps reading 100 °C because the heat supplied is used to

  1. overcome intermolecular attraction Correct answer.
  2. increase the specific heat of water
  3. raise the temperature of the vapour
  4. increase the kinetic energy of the molecules

Explanation

At the boiling point the heat supplied acts as latent heat of vaporisation and is spent in pulling molecules apart against their mutual attraction. The average kinetic energy of the molecules, and hence the thermometer reading, therefore does not change until all the water has boiled away.

Question 26Heat and Thermal Phenomena

A bimetallic strip is made by riveting a brass strip and an iron strip together. Brass expands more than iron for the same temperature rise. When the strip is heated, it bends

  1. towards brass, with iron on the outer side
  2. towards iron, with brass on the outer side Correct answer.
  3. it remains straight because both metals expand
  4. towards iron, with brass on the inner side

Explanation

Brass has the larger coefficient of linear expansion, so on heating it becomes longer than the iron strip riveted to it. The longer brass strip must form the outer, convex arc of the bend, and the strip therefore curves towards the iron.

Question 27Heat and Thermal Phenomena

In summer, water kept in a bottle wrapped in a wet cloth stays cooler than water in an unwrapped bottle because

  1. water in the cloth conducts heat out of the bottle
  2. the cloth stops heat from reaching the bottle by conduction
  3. evaporation of water takes latent heat from the bottle Correct answer.
  4. the wet cloth reflects the sunlight away from the bottle

Explanation

Water evaporating from the cloth must absorb latent heat of vaporisation, and it takes this heat from the bottle and the water inside it. The bottle therefore loses heat continuously and its contents stay cooler than the surrounding air.

Question 28Heat and Thermal Phenomena

50 g of water at 80 °C is mixed with 50 g of water at 20 °C in an insulated container. The final temperature of the mixture is

  1. 60 °C
  2. 40 °C
  3. 50 °C Correct answer.
  4. 100 °C

Explanation

In an insulated container the heat lost by the hot water equals the heat gained by the cold water. Since the masses and the substance are the same, the final temperature lies midway between 80 °C and 20 °C, which is 50 °C.

Question 29Heat and Thermal Phenomena

What is the total heat needed to convert 10 g of ice at 0 °C into water at 20 °C? (Latent heat of fusion of ice = 80 cal/g, specific heat capacity of water = 1 cal/(g·°C))

  1. 200 cal
  2. 1000 cal Correct answer.
  3. 800 cal
  4. 820 cal

Explanation

Melting 10 g of ice requires mL = 10 × 80 = 800 cal. Warming the resulting water from 0 °C to 20 °C requires mcΔT = 10 × 1 × 20 = 200 cal. The total heat needed is therefore 800 + 200 = 1000 cal.

Question 30Heat and Thermal Phenomena

A metal ball just passes through a metal ring at room temperature. The ball alone is now heated and placed on the ring. Which statement is correct?

  1. It does not pass, because the ball and the ring expand equally
  2. It does not pass, because the ball expands but the ring does not Correct answer.
  3. It passes, because the hole in the ring also grows when the ball is heated
  4. It passes through more easily, because heating makes the metal softer

Explanation

Heating the ball increases its diameter through thermal expansion, while the ring stays at room temperature and keeps its original opening. The ball is therefore now too large to pass through the ring, which is the same effect that makes a tight metal lid loosen when it is warmed.

Question 31Heat and Thermal Phenomena

At the same room temperature, a metal spoon kept beside a wooden spoon feels colder to touch. The correct reason is that

  1. metal conducts heat away from the skin faster than wood does Correct answer.
  2. the metal spoon is at a lower temperature than the wooden spoon
  3. wood absorbs heat from the surrounding air and becomes warm
  4. the metal spoon radiates heat towards the hand more strongly

Explanation

Both spoons are at room temperature; the sensation of coldness depends on how quickly heat leaves the skin. Metals are good conductors of heat because of freely moving electrons, so heat flows from the finger into the metal rapidly and the finger feels cold. Wood is a poor conductor, so heat is drawn away slowly and the spoon feels comparatively warm.

Question 32Heat and Thermal Phenomena

A room air conditioner is fixed high up on the wall near the ceiling rather than near the floor because

  1. cold air rises upwards and then spreads through the whole room
  2. cool air is denser, so it sinks and cools the room through convection Correct answer.
  3. heat is removed from the ceiling mainly by radiation
  4. air near the ceiling is always at a higher pressure than air near the floor

Explanation

Air cooled by the unit contracts, becomes denser and sinks, while the warmer air below rises to take its place. This sets up convection currents that circulate the cooled air through the whole room. If the unit were placed near the floor, the cold air would stay in the lower part and the upper part would remain warm.

Question 33Heat and Thermal Phenomena

Steam at 100 °C causes a more severe burn on the skin than boiling water at 100 °C because steam

  1. is at a much higher temperature than boiling water
  2. releases latent heat of vaporisation on condensing Correct answer.
  3. transfers heat to the skin mainly by convection
  4. has a lower specific heat capacity than water

Explanation

When steam at 100 °C touches the skin it condenses into water at 100 °C, and in doing so gives up its large latent heat of vaporisation (about 2260 J per gram). Boiling water at the same temperature releases only the heat given out while cooling. The extra latent heat is why a steam burn is far more damaging.

Question 34Heat and Thermal Phenomena

Two identical cups A and B hold water at 80 °C and 60 °C respectively and are kept in the same room. During the first minute,

  1. both cups cool by exactly the same amount
  2. cup B cools faster because it is nearer to room temperature
  3. neither cup cools until both reach the same temperature
  4. cup A cools faster, as its excess temperature is larger Correct answer.

Explanation

Newton's law of cooling states that the rate of loss of heat is proportional to the difference between the temperature of the body and that of the surroundings. Cup A starts 80 °C above a room at, say, 30 °C, so its excess temperature is larger than that of cup B. Hence the hotter cup cools at the greater rate at the start, though its rate falls as it approaches room temperature.

Question 35Heat and Thermal Phenomena

Two identical cans are filled with equal amounts of hot water at the same temperature. One is painted dull black and the other is polished white, and both are kept in the same room. The black can cools faster because

  1. black paint lowers the specific heat capacity of the water
  2. black surfaces are better emitters of radiation than white surfaces Correct answer.
  3. black surfaces reflect radiation better than white surfaces
  4. white paint conducts heat away more slowly than black paint

Explanation

A dull black surface is a good absorber and also a good emitter of thermal radiation, whereas a polished white surface absorbs and emits poorly. The black can therefore radiates heat to the surroundings at a greater rate and its water cools faster. This is the same property that makes black containers better absorbers of solar heat.

Question 36Heat and Thermal Phenomena

Equal masses of water and kerosene at the same initial temperature are heated by identical heaters for the same time. The kerosene shows a larger rise in temperature. The correct inference is that

  1. the heater supplied more heat energy to the kerosene
  2. water can absorb heat only by convection
  3. kerosene has a much higher boiling point than water
  4. kerosene has a smaller specific heat capacity than water Correct answer.

Explanation

For the same mass and the same heat supplied, the temperature rise is inversely proportional to the specific heat capacity, since Q = mcΔT. The liquid that shows the larger rise for the same heat has the smaller specific heat capacity. This agrees with the known values: about 2100 J/(kg °C) for kerosene against 4200 J/(kg °C) for water.

Question 37Refraction of Light and Lenses

A transparent medium slows light down to 2.0 × 10⁸ m/s. Taking the speed of light in vacuum as 3.0 × 10⁸ m/s, the absolute refractive index of the medium is closest to:

  1. 1.0
  2. 0.67
  3. 1.5 Correct answer.
  4. 3.0

Explanation

The absolute refractive index is defined as n = c/v, where c is the speed of light in vacuum and v is the speed in the medium. Substituting gives n = (3.0 × 10⁸)/(2.0 × 10⁸) = 1.5, a value typical of glass. Since the medium slows light, n must be greater than 1.

Question 38Refraction of Light and Lenses

A lens is thicker at its centre than at its edges and brings a parallel beam of light to a real focus. Such a lens is called:

  1. a bifocal lens
  2. a concave lens
  3. a cylindrical lens
  4. a convex lens Correct answer.

Explanation

A lens that is thicker at the centre converges a parallel beam to a real point focus and is therefore a convex, or converging, lens. A concave lens is thinner at the centre and spreads the beam out instead.

Question 39Refraction of Light and Lenses

The SI unit of the power of a lens is the:

  1. metre
  2. dioptre Correct answer.
  3. dioptre per metre
  4. candela

Explanation

Power is defined as P = 1/f with the focal length f measured in metres, so its unit is the reciprocal metre, called the dioptre (D). A converging lens of focal length 1 m therefore has a power of +1 D.

Question 40Refraction of Light and Lenses

An object is placed 20 cm from a convex lens of focal length 10 cm. Where is the image formed and what is its nature?

  1. 10 cm on the other side of the lens, real and inverted
  2. 20 cm on the other side of the lens, real and inverted Correct answer.
  3. 30 cm on the other side of the lens, real and inverted
  4. 20 cm on the same side as the object, virtual and erect

Explanation

Using 1/v − 1/u = 1/f with u = −20 cm and f = +10 cm gives 1/v = 1/10 − 1/20 = 1/20, so v = +20 cm. A positive v places the image on the opposite side of the lens, and m = v/u = −1 shows it is real, inverted and the same size as the object, since the object lies at 2F.

Question 41Refraction of Light and Lenses

An object 5 cm tall is placed 15 cm from a convex lens of focal length 10 cm. The image formed is:

  1. 30 cm tall and inverted
  2. 10 cm tall and inverted Correct answer.
  3. 10 cm tall and erect
  4. 2.5 cm tall and erect

Explanation

With u = −15 cm and f = +10 cm, 1/v = 1/10 − 1/15 = 1/30, so v = +30 cm. Magnification m = v/u = 30/(−15) = −2, so the image height is 2 × 5 cm = 10 cm and the negative sign shows the image is inverted.

Question 42Refraction of Light and Lenses

A convex lens of power +5 D is placed in contact with a concave lens of power −2 D. The combination has:

  1. power +3 D and focal length 3 cm, converging
  2. power −3 D and focal length 33.3 cm, diverging
  3. power +7 D and focal length 14.3 cm, converging
  4. power +3 D and focal length 33.3 cm, converging Correct answer.

Explanation

For thin lenses in contact the powers add algebraically: P = (+5 D) + (−2 D) = +3 D. The focal length is f = 1/P = 1/3 m ≈ 33.3 cm, and a positive power means the combination converges light.

Question 43Refraction of Light and Lenses

A ray of light inside a glass block of refractive index 1.5 strikes the glass–air boundary. Total internal reflection occurs only when:

  1. the angle of incidence in glass is less than the critical angle
  2. the angle of incidence in glass exceeds the critical angle Correct answer.
  3. the ray passes from air into glass at a large angle of incidence
  4. the angle of refraction in air becomes greater than 90°

Explanation

For glass of n = 1.5, sin C = 1/n = 0.667, giving a critical angle of about 42°. Total internal reflection happens only when light travels from the denser glass towards the rarer air and the angle of incidence in the glass is greater than C, so that no refracted ray exists.

Question 44Refraction of Light and Lenses

A ray of light passes obliquely through a rectangular glass slab and emerges from the opposite face. Which statement describes the emergent ray?

  1. It bends away from the normal and meets the incident ray inside the slab.
  2. It is parallel to the incident ray but shifted sideways. Correct answer.
  3. It emerges perpendicular to the direction of the incident ray.
  4. It follows exactly the same straight-line path as the incident ray.

Explanation

At the first surface the ray bends towards the normal, and at the second parallel surface it bends away by an equal amount, so the emergent ray is parallel to the incident ray. Because the two refractions happen at different points, the ray is shifted sideways, a shift called lateral displacement, which grows with slab thickness and refractive index.

Question 45Refraction of Light and Lenses

A thin convex lens made of glass of refractive index 1.5 is immersed in a liquid that also has refractive index 1.5. The lens then:

  1. has a focal length half of its value in air.
  2. behaves like a plane-parallel glass plate. Correct answer.
  3. has a focal length twice its value in air, so it converges less.
  4. behaves like a concave lens of the same focal length.

Explanation

The lens maker's formula contains the factor (n_lens/n_medium − 1). When the lens and the surrounding medium have equal refractive indices this factor becomes zero, so the focal length becomes infinite. The lens then has no converging or diverging action and simply behaves like a plane-parallel glass plate.

Question 46Refraction of Light and Lenses

An object is placed 10 cm in front of a concave lens of focal length 15 cm. The image formed is:

  1. 6 cm on the opposite side of the lens, real and inverted
  2. 30 cm on the same side as the object, virtual and erect
  3. 6 cm on the same side as the object, virtual and erect Correct answer.
  4. 30 cm on the opposite side of the lens, real and inverted

Explanation

For a concave lens f = −15 cm and u = −10 cm, so 1/v = 1/f + 1/u = −1/15 − 1/10 = −1/6, giving v = −6 cm. The negative sign places the image on the same side as the object, and m = v/u = +0.6 shows the image is virtual, erect and diminished.

Question 47Refraction of Light and Lenses

A ray of light travelling in air strikes the surface of a glass block obliquely and enters the glass. How does the ray change direction at the air–glass boundary, and why?

  1. It bends towards the normal because glass is optically denser than air. Correct answer.
  2. It continues in the same straight line because both media are transparent.
  3. It bends towards the normal because glass is optically rarer than air.
  4. It bends away from the normal because glass is optically denser than air.

Explanation

When light passes obliquely from a rarer medium (air) into a denser medium (glass), it slows down and bends towards the normal drawn at the point of incidence. The refractive index of glass is greater than that of air, so the angle of refraction is smaller than the angle of incidence.

Question 48Refraction of Light and Lenses

A narrow beam of white light is passed through a glass prism and falls on a screen. Which coloured component is deviated the most from the original direction?

  1. Violet Correct answer.
  2. Red
  3. Green
  4. Yellow

Explanation

The prism disperses white light because the refractive index of glass is different for different wavelengths. Violet light has the shortest wavelength and the largest refractive index in glass, so it is deviated the most, while red is deviated the least.

Question 49Refraction of Light and Lenses

Stars appear to twinkle at night, while planets generally do not. The twinkling of stars is mainly caused by:

  1. Reflection of starlight from clouds in the atmosphere
  2. Continuous refraction of starlight through layers of the atmosphere of changing density Correct answer.
  3. Total internal reflection of starlight inside the ionosphere
  4. Dispersion of starlight by water vapour in the air

Explanation

The atmosphere is not uniform; its density and refractive index change continuously with height and with temperature. Starlight passing through these shifting layers bends by varying amounts, so the apparent position and brightness of the star fluctuate, producing twinkling. Planets are much closer and behave as extended sources, so the variations average out.

Question 50Refraction of Light and Lenses

A ray of light passes from air into a glass block of refractive index 1.5. If the angle of incidence is 30°, what is the angle of refraction (to the nearest degree)?

  1. 19° Correct answer.
  2. 60°
  3. 30°
  4. 49°

Explanation

By Snell's law, n = sin i / sin r, so sin r = sin 30° / 1.5 = 0.5 / 1.5 = 0.333. The angle whose sine is 0.333 is approximately 19.5°, which rounds to 19°. The ray therefore bends towards the normal as expected when entering a denser medium.