ICSE Class 8 Physics Sample Paper with Solutions Set 03

Question 1

Choose the correct answer out of the four available choices given under each question. [15]

1. Electric charges can flow through [1 Mark]
(a) Both conductors and insulators
(b) Insulators
(c) Conductors
(d) Neither conductors nor insulators

Answer: (C) Conductors

Electric charges can flow freely through conductors, whereas insulators do not allow charges to flow through them.

Teacher's Note:
a) Remember that metals and ionic solutions are typical conductors of electricity due to free electrons or ions.
b) Do not confuse the ability to hold a static charge with the ability to allow electric charges to flow continuously.

2. A freely suspended magnet would come to rest in the [1 Mark]
(a) East west direction
(b) North south direction
(c) South east direction
(d) North west direction

Answer: (B) North south direction

A freely suspended bar magnet always aligns itself along the geographic north-south direction under the influence of Earth's magnetic field.

Teacher's Note:
a) The magnetic north pole of a suspended magnet points towards the geographic north pole of the Earth.
b) Ensure you distinguish between geographic poles and magnetic poles when explaining this behavior.

3. The change of state from vapour to liquid at a constant temperature is called [1 Mark]
(a) Fusion
(b) Vapourisation
(c) Freezing
(d) Condensation

Answer: (D) Condensation

Condensation is the phase transition in which a substance changes from its gaseous or vapour state into liquid state at a constant temperature.

Teacher's Note:
a) Fusion refers to solid turning into liquid, whereas vaporization is liquid turning into gas.
b) Note that temperature remains constant during any phase change as heat energy is used to change intermolecular forces.

4. The type of lens used as a magnifying glass [1 Mark]
(a) Concave lens
(b) Convex lens
(c) Concavo-convex lens
(d) Convexo-concave lens

Answer: (B) Convex lens

A convex lens forms a virtual, erect, and magnified image of an object when the object is placed within its focal length.

Teacher's Note:
a) Convex lenses are thicker at the center and thinner at the edges, converging light rays.
b) Concave lenses always produce virtual, erect, and diminished images, hence they cannot be used as magnifying glasses.

5. Our solar system belongs to the [1 Mark]
(a) Seyfert galaxy
(b) Milky way galaxy
(c) Whirl pool galaxy
(d) Andromeda galaxy

Answer: (B) Milky way galaxy

Our solar system is a part of the Milky Way galaxy, which is a barred spiral galaxy.

Teacher's Note:
a) The Milky Way contains hundreds of billions of stars along with gas and dust.
b) Andromeda is the nearest major galaxy to our Milky Way galaxy.

6. If the weight of a body is more than the weight of fluid displaced by it, then the body [1 Mark]
(a) Sinks
(b) Floats
(c) First floats and then sinks
(d) None of these

Answer: (A) Sinks

When downward gravitational force (weight of the body) exceeds upward buoyant force (weight of displaced fluid), the net force is downward, causing the body to sink.

Teacher's Note:
a) A body floats when its weight is equal to or less than the weight of the fluid displaced.
b) Sinking occurs when the density of the object is greater than the density of the fluid.

7. Air in motion possesses [1 Mark]
(a) Potential energy
(b) Kinetic energy
(c) Electrical energy
(d) Geothermal energy

Answer: (B) Kinetic energy

Air in motion (wind) possesses kinetic energy due to the mass and velocity of the moving air molecules.

Teacher's Note:
a) Any object in motion possesses kinetic energy, calculated as half of mass times velocity squared.
b) Wind mills harness this kinetic energy of moving air to generate useful work or electricity.

8. When a positively charged body is brought close to another positively charged body, it will show [1 Mark]
(a) Attraction
(b) Repulsion
(c) No effect
(d) None of these

Answer: (B) Repulsion

Like charges repel each other, so two positively charged bodies will experience a repulsive force when brought close together.

[Figure: Two positively charged bodies experiencing outward repulsive forces away from each other]

Teacher's Note:
a) Fundamental law of electrostatics states that like charges repel and unlike charges attract.
b) Ensure students do not confuse gravitational attraction with electrostatic forces between like charges.

9. The Earth’s magnetic field is maximum [1 Mark]
(a) At the poles of the Earth
(b) At the centre of Earth
(c) At the outer surface of the Earth
(d) None of these

Answer: (A) At the poles of the Earth

Earth's magnetic field lines are crowded near the magnetic poles, indicating that the magnetic field strength is maximum at the poles.

Teacher's Note:
a) Magnetic field intensity is weakest near the magnetic equator and strongest near the poles.
b) Compass needles dip vertically downwards at the magnetic poles.

10. Speed of light is maximum in [1 Mark]
(a) Air
(b) Water
(c) Glass
(d) Vacuum

Answer: (D) Vacuum

Light travels at its maximum possible speed, approximately \( 3 \times 10^{8} \text{ m/s} \), in a vacuum where there is no obstructing medium.

Teacher's Note:
a) As the optical density of a medium increases, the speed of light through it decreases.
b) The refractive index is the ratio of the speed of light in vacuum to that in a given medium.

11. Land breeze blows [1 Mark]
(a) During the day
(b) During the night
(c) Both during day and night
(d) None of the above

Answer: (B) During the night

Land cools down faster than the sea at night, creating high pressure over land and low pressure over the sea, causing wind to blow from land to sea.

Teacher's Note:
a) Sea breeze blows during the day when land heats up faster than water.
b) Convection currents in coastal regions are driven by differential heating of land and water.

12. An image which can be captured on a screen is called [1 Mark]
(a) Erect
(b) Inverted
(c) Virtual
(d) Real

Answer: (D) Real

A real image is formed when light rays actually intersect after reflection or refraction, and it can always be projected onto a screen.

Teacher's Note:
a) Virtual images cannot be caught on a screen because light rays only appear to diverge from the image position.
b) Real images formed by lenses and mirrors are typically inverted with respect to the object.

13. Liquid pressure is measured by [1 Mark]
(a) Anemometer
(b) Odometer
(c) Manometer
(d) Barometer

Answer: (C) Manometer

A manometer is a scientific instrument used to measure liquid pressure or gas pressure differences.

Teacher's Note:
a) Barometers are used to measure atmospheric pressure.
b) Anemometers measure wind speed, and odometers measure distance traveled by vehicles.

14. The direction of buoyant force is always [1 Mark]
(a) Vertically downward
(b) Vertically upward
(c) Along the surface
(d) At any angle with the surface of liquid

Answer: (B) Vertically upward

Buoyant force arises from the pressure difference at different depths in a fluid, acting always in a direction opposite to gravity, which is vertically upward.

Teacher's Note:
a) The upward buoyant force opposes the weight of the immersed object.
b) The magnitude of buoyant force equals the weight of the fluid displaced by the object (Archimedes' Principle).

15. Small insects like water striders can walk on water due to [1 Mark]
(a) Surface tension
(b) Strong feet
(c) Elastic tension
(d) Attraction between feet and water

Answer: (A) Surface tension

Surface tension creates an elastic skin-like property on the free surface of water, supporting small weights like insects without letting them sink.

Teacher's Note:
a) Cohesive forces among water molecules at the surface are responsible for surface tension.
b) If the weight of the insect exceeds the upward force due to surface tension, the insect will break through and sink.

Question 2

(A) Match the columns and rewrite them correctly. [5]

Answer:
1. 1 Calorie - 4.2 Joules
2. Concave lens - Myopia
3. Silver - Conductor
4. Water in a dam - Hydroelectric energy
5. Relative density - No unit

Teacher's Note:
a) Relative density is a ratio of two similar quantities (density of substance to density of water), hence it has no units.
b) Concave lenses diverge light and are prescribed to correct myopia (short-sightedness).

(B) Fill up the blanks and rewrite the sentences: [5]
1. The space around a magnet where its influence can be felt is called ____________.
2. ____________ protects buildings from the damage caused by lightning.
3. Water is used as a ____________ in thermal power stations.
4. A ray of light passing through ____________ of a lens passes undeviated.
5. The force of attraction between molecules of the same substance is called ____________.

Answer:
1. Magnetic field
2. Lightning conductor
3. Coolant
4. Optical centre
5. Cohesion

Teacher's Note:
a) Ensure exact terminology is used; for example, cohesion refers to same-substance molecules, whereas adhesion refers to different substances.
b) A ray passing through the optical centre of any thin lens suffers no deviation in its path.

Question 3

(A) State whether the following statements are true or false. Correct the false statement and rewrite it. [5]
1. Earth is the largest planet of the solar system.
2. In an electric motor, mechanical energy is converted into electrical energy.
3. Good conductors have excess of free electrons.
4. Convex lenses are always tapering in the middle and thicker at their edges.
5. During vapourisation, temperature of a liquid remains constant.

Answer:
1. False. Jupiter is the largest planet of the solar system.
2. False. In an electric motor, electrical energy is converted into mechanical energy. (Note: The official key states this statement is false because an electric motor converts electrical energy into mechanical energy; if taken as printed in the question paper, it describes a motor correctly. We follow the official key text.)
3. True.
4. False. Convex lenses are always tapering at the edges and thicker at their middle.
5. True.

Teacher's Note:
a) Jupiter is the largest planet, while Mercury is the smallest planet in our solar system.
b) A convex lens is thicker at the centre and thinner at the edges, unlike a concave lens.

(B) Give reasons for the following: [5]
1. A gas can be easily compressed.
2. Dispersion of light occurs when it passes through a prism.
3. Kilometre is not a convenient unit to measure distances in the universe.
4. A piece of tile or stone feels colder than a piece of wood, even though both are at the same temperature.
5. A normal atom is electrically neutral though it contains charged particles like electrons and protons.

Answer:
1. Molecules of gases are very far apart and there is a lot of empty space between them, so a gas can be easily compressed.
2. Dispersion of light occurs when it passes through a prism because different colours of white light travel at different speeds and are refracted through different angles.
3. Kilometre is not a convenient unit to measure distances in the universe because heavenly bodies are extremely far from each other, requiring larger units like light-years.
4. A piece of tile or stone is a good conductor of heat compared to wood, so it conducts heat away from our hand faster, making it feel colder.
5. In a normal atom, the number of negatively charged electrons is equal to the number of positively charged protons, balancing the charges and making it electrically neutral.

Teacher's Note:
a) Conduction rates determine how fast thermal energy flows from our body to objects.
b) Astronomical distances are immense, which is why light-year is preferred over kilometres.

Question 4

(A)
1. Define: [2]
(a) Refraction of light
(b) Angle of refraction
(c) Angle of incidence

Answer:
(a) Refraction of light: When light travels from one transparent medium to another transparent medium, it bends from its original path. This phenomenon of bending of light is called refraction.
(b) Angle of refraction: The angle formed between the refracted ray and the normal at the point of incidence is called the angle of refraction.
(c) Angle of incidence: The angle formed between the incident ray and the normal at the point of incidence is called the angle of incidence.

Teacher's Note:
a) Always measure angles with respect to the normal drawn perpendicular to the interface.
b) Refraction is caused by the change in the speed of light when passing from one optical medium to another.

2. Define surface tension. Give two examples where surface tension is seen. [3]

Answer:
Surface tension is the property of a liquid by virtue of which its free surface behaves like a stretched membrane with a tendency to contract and acquire minimum surface area.
Examples:
1. Soaps and detergents help in cleaning clothes as they lower the surface tension of water, allowing water to soak into the pores of clothes efficiently.
2. Small insects like the water strider can walk on water because their weight is not enough to penetrate the surface tension of water.

Teacher's Note:
a) Surface tension results from the inward cohesive forces acting on molecules at the liquid surface.
b) Adding detergents breaks these cohesive forces, reducing surface tension for better wetting action.

(B)
1. What is an electroscope? Name two kinds of electroscopes. [2]

Answer:
An electroscope is a device used to detect whether a body is charged or uncharged and to identify the nature of charge on it.
The two kinds of electroscopes are:
1. Pith ball electroscope
2. Gold leaf electroscope

Teacher's Note:
a) Gold leaf electroscopes are more sensitive and can measure the magnitude of charge qualitatively.
b) Pith ball electroscopes use the principle of repulsion between like charges.

2. Draw field lines when two bar magnets are placed with their opposite poles facing each other. List any two properties of magnetic field lines. [3]

Answer:
[Figure: Two bar magnets placed with South (S) and North (N) poles facing each other, showing continuous magnetic field lines curving from North to South pole across the gap]
Properties of magnetic field lines:
1. Magnetic field lines originate from the North Pole and terminate at the South Pole outside the magnet.
2. Magnetic field lines never intersect each other.

Teacher's Note:
a) Unlike poles facing each other attract, so field lines run directly from one magnet to the other.
b) If two field lines intersected, it would mean the magnetic compass needle points in two directions at the same point, which is impossible.

Question 5

(A)
1. Differentiate between renewable and non-renewable sources of energy with one example for each. [2]

Answer:

Teacher's Note:
a) Renewable energy sources are environmentally sustainable and inexhaustible on a human timescale.
b) Non-renewable sources take millions of years to form and cause pollution when burned.

2. What is heat? State three factors on which the amount of heat gained or lost by a body depends. [3]

Answer:
Heat is a form of energy which brings about the sensation of hotness or coldness in us.
The amount of heat gained or lost by a body depends on:
1. Mass of the substance
2. Rise or fall in temperature of the substance
3. Nature of the substance (specific heat capacity)

Teacher's Note:
a) Heat always flows from a body at a higher temperature to a body at a lower temperature.
b) The formula \( Q = mc\Delta t \) summarises how mass, specific heat, and temperature change affect heat energy.

(B)
1. Write any six characteristics of matter and its constituent particles. [3]

Answer:
1. Matter is made up of tiny particles known as atoms which consist of three particles called protons, electrons, and neutrons.
2. Protons carry a positive charge, electrons carry a negative charge, and neutrons carry no charge, making an atom electrically neutral.
3. The central part of the atom consisting of protons and neutrons is called the nucleus.
4. Electrons revolve around the nucleus in circular paths called orbits or shells.
5. Electrons present in the outermost orbit are called valence electrons or free electrons.
6. The number of protons equals the number of electrons, making the total positive charge equal to the total negative charge.

Teacher's Note:
a) Matter occupies space and has mass due to its constituent particles.
b) Valence electrons are responsible for chemical bonding and electrical conduction.

2. State the uses of a convex lens. [2]

Answer:
1. It is used in optical instruments like cameras, projectors, telescopes, and microscopes.
2. It is used as a reading lens and as a magnifying glass.
3. It is used in spectacles for the correction of long-sightedness (hypermetropia).

Teacher's Note:
a) Convex lenses converge parallel rays of light to a focal point.
b) They produce magnified virtual images when objects are placed within their focal length.

Question 6

(A)
1. Differentiate between: [3]
(a) Planets and satellites
(b) Stars and planets

Answer:
(a)

(b)

Teacher's Note:
a) Stars generate their own energy through nuclear fusion in their cores.
b) Planets only reflect the light received from their parent star.

2. Give two consequences of high latent heat of steam. [2]

Answer:
1. Steam is used for running trains and industrial machines because the high amount of heat contained in it can be efficiently turned into mechanical energy.
2. Water from the soil does not evaporate quickly by the heat of the Sun because of water's high specific latent heat of vaporization, thus protecting plants from wilting.

Teacher's Note:
a) Latent heat of vaporization is the heat required to change liquid into vapor without temperature change.
b) Steam causes more severe burns than boiling water at the same temperature due to this extra latent heat.

(B)
1. Name the two factors on which buoyant force depends. State the relationship between the buoyant force on an object and the weight of a liquid displaced by it? [2]

Answer:
The two factors on which buoyant force depends are:
1. Volume of the object immersed in the fluid.
2. Density of the fluid.
Relationship: The buoyant force on an object is equal to the weight of the liquid displaced by the object.

Teacher's Note:
a) This relationship is the core statement of Archimedes' Principle.
b) Greater volume immersion or higher fluid density increases the buoyant force.

2. Define the following: [3]
(a) Conduction
(b) Principal axis
(c) Valence electrons

Answer:
(a) Conduction: Conduction is the process of heat transmission in which heat energy is transferred from one atom to another in the direction of lower temperature, without actual movement of atoms from their mean positions.
(b) Principal axis: Principal axis is a straight line passing through the optical centre of the lens and perpendicular to both the faces of the lens.
(c) Valence electrons: The electrons present in the outermost orbit of an atom are known as valence electrons.

Teacher's Note:
a) Conduction is the primary mode of heat transfer in solids.
b) The principal axis serves as the reference line for measuring all optical distances in lenses.

Question 7

(A)
1. A coil of insulated wire is connected to a galvanometer. What would be seen if a bar magnet brought towards one face of the coil is: [3]
(a) Moved quickly towards it? What does the change indicate?
(b) Moved quickly away from it?
(c) Name the phenomena involved and explain it.

Answer:
(a) A momentary deflection in the galvanometer to one side is seen. This indicates the presence of an induced electric current.
(b) Momentary deflection in the galvanometer to the opposite direction is seen, showing the presence of current in the reverse direction.
(c) The phenomenon involved is electromagnetic induction. It is the property by which a changing magnetic field within a closed conducting coil induces an electric current in the coil.

Teacher's Note:
a) Electromagnetic induction was discovered by Michael Faraday.
b) Motion between the magnetic field and the coil is essential to induce current.

2. State the characteristics of liquid pressure. [2]

Answer:
1. Liquid pressure increases with depth.
2. Liquid pressure remains the same in all directions at a given depth.
3. Liquid pressure depends upon the density of the liquid.
4. Liquids exert pressure on the sides of the container they are stored in.
5. A liquid seeks its own level.

Teacher's Note:
a) Liquid pressure acts equally in all directions at any specific point inside the liquid.
b) Pressure does not depend on the shape or cross-sectional area of the container.

(B)
1. What are constellations? Name any three constellations. [2]

Answer:
A group of stars forming a particular pattern or recognizable shape in the sky is called a constellation.
Three constellations are:
1. Orion
2. Ursa Major
3. Scorpio

Teacher's Note:
a) Constellations help astronomers map and locate regions of the night sky easily.
b) Stars in a constellation are not necessarily physically connected; they only appear close from Earth's perspective.

2. State the type of lens used to get a [3]
(a) Virtual and diminished image of an object
(b) Real and diminished image of an object
Justify your answers in the above two cases by drawing ray diagrams.

Answer:
(a) Concave lens is used to get a virtual and diminished image of an object.
(b) Convex lens is used to get a real and diminished image of an object.

[Figure: Ray diagram showing a concave lens forming a virtual, erect, and diminished image between optical centre and focus for any object position]
[Figure: Ray diagram showing a convex lens forming a real, inverted, and diminished image between focus and 2F on the other side when the object is placed beyond 2F]

Teacher's Note:
a) Concave lenses always produce virtual, upright, and diminished images regardless of object distance.
b) A convex lens produces a real, inverted, and diminished image only when the object is placed beyond twice the focal length (\( 2F \)).