ICSE Class 8 Physics Sample Paper with Solutions Set 04

Question 1
Choose the correct answer out of the four available choices given under each question. [15]

1. Which of the following is not a property of magnetic lines of force? [1 Mark]
(a) Each line is a closed and continuous curve
(b) They originate at the North Pole
(c) They never intersect each other
(d) They are crowded near the centre of the magnet

Answer: (d) They are crowded near the centre of the magnet

The magnetic lines of force are crowded near the poles of a magnet as the field is strongest at the poles, not the centre.

Teacher's Note:
a) Magnetic field lines always form closed continuous curves extending from North to South pole outside the magnet.
b) Students often confuse the region of maximum field strength (poles) with the geometric center of the magnet.

2. A lightning streak is a type of [1 Mark]
(a) Electric discharge
(b) Electrostatic repulsion
(c) Electrostatic attraction
(d) None of the above

Answer: (a) Electric discharge

Accumulation of charges in clouds leads to an electric discharge through the air, producing lightning.

Teacher's Note:
a) Lightning is a sudden electrostatic discharge that occurs during an electrical thunderstorm.
b) Make sure to distinguish between charge accumulation and the actual discharge process.

3. If the density of an object is greater than the density of the liquid in which the body is kept, then the object will [1 Mark]
(a) Float on liquid
(b) Sink in liquid
(c) Partially sink in liquid
(d) Can’t predict on the basis of the density alone

Answer: (b) Sink in liquid

An object sinks if its density exceeds the density of the fluid.

Teacher's Note:
a) The condition for sinking is object density greater than fluid density (\( \rho_{\text{object}} \gt \rho_{\text{fluid}} \)).
b) If densities are equal, the body floats completely immersed anywhere inside the liquid.

4. The force of attraction between molecules of similar kind is called [1 Mark]
(a) Force of adhesion
(b) Intramolecular force of repulsion
(c) Force of cohesion
(d) Intermolecular force of adhesion

Answer: (c) Force of cohesion

Cohesion is the intermolecular attraction between like molecules.

Teacher's Note:
a) Cohesive forces hold molecules of the same substance together.
b) Adhesive forces act between molecules of different substances.

5. The distance of the lens from the film of a camera can be changed by turning the [1 Mark]
(a) Focusing ring
(b) Diaphragm
(c) Shutter
(d) View finder

Answer: (a) Focusing ring

Turning the focusing ring adjusts the lens position to form a sharp image on the film.

Teacher's Note:
a) The focusing ring alters the lens-to-film distance for objects at various distances.
b) The diaphragm controls the amount of light entering the camera.

6. The angle between the incident ray and the emergent ray of a prism is called [1 Mark]
(a) Angle of emergence
(b) Angle of incidence
(c) Angle of deviation
(d) Angle of refraction

Answer: (c) Angle of deviation

The angle by which the emergent ray deviates from the direction of the incident ray is the angle of deviation.

Teacher's Note:
a) Angle of deviation measures the total bending of light caused by the prism.
b) Do not confuse it with the angle of refraction inside the prism.

7. Which of the following feature does not hold true for a fuse? [1 Mark]
(a) It has a low melting point
(b) It has high resistance
(c) It is used to break circuits when a large current flows
(d) It is used at the end of any household circuit

Answer: (d) It is used at the end of any household circuit

A fuse is always connected at the beginning of a household circuit (live wire) to protect all appliances.

Teacher's Note:
a) Fuses must have high resistance and low melting point.
b) Placing a fuse at the end of a circuit would leave the main wiring unprotected.

8. Which among these is not a type of coal? [1 Mark]
(a) Bituminous
(b) Anthracite
(c) Asphalt
(d) Lignite

Answer: (c) Asphalt

Asphalt is a petroleum product, whereas anthracite, bituminous, and lignite are varieties of coal.

Teacher's Note:
a) The main types of coal in increasing order of carbon content are lignite, bituminous, and anthracite.
b) Asphalt is commonly used in road construction.

9. Which among these is not a non-renewable source of energy? [1 Mark]
(a) Natural gas
(b) Biogas
(c) Forests
(d) Coal

Answer: (b) Biogas

Biogas is a renewable source of energy generated from organic waste.

Teacher's Note:
a) Natural gas, coal, and petroleum are finite fossil fuels (non-renewable).
b) Forests are technically renewable if managed sustainably, but biogas is explicitly a renewable fuel.

10. The heat required to change the state of a substance without any change in temperature is [1 Mark]
(a) Specific latent heat
(b) Specific heat capacity
(c) Thermal heat capacity
(d) State heat capacity

Answer: (a) Specific latent heat

Latent heat is absorbed or released during a phase change at constant temperature.

Teacher's Note:
a) Specific latent heat refers to unit mass undergoing a phase change.
b) Specific heat capacity causes a rise in temperature without a change of state.

11. The image formed by a convex lens is observed to be virtual, erect and larger than the object. Hence, the position of the object should be [1 Mark]
(a) Between the focus and the centre of curvature
(b) At the centre of curvature
(c) Beyond the centre of curvature
(d) Between the optical centre and the focus

Answer: (d) Between the optical centre and the focus

A convex lens produces a magnified virtual and erect image only when the object lies within the focal length.

[Figure: Ray diagram showing an object placed between optical centre \( O \) and focus \( F_1 \) of a convex lens, forming a virtual, erect, and enlarged image \( A'B' \) on the same side.]

Teacher's Note:
a) This is the principle behind a simple microscope (magnifying glass).
b) All other positions for a real object produce real and inverted images.

12. Which among the following is not a natural satellite of any planet? [1 Mark]
(a) Ceres
(b) Phobos
(c) Deimos
(d) Moon

Answer: (a) Ceres

Ceres is a dwarf planet located in the asteroid belt, not a satellite.

Teacher's Note:
a) Phobos and Deimos are moons of Mars, and the Moon orbits Earth.
b) Ceres was reclassified from an asteroid to a dwarf planet.

13. Which among the following is not true for a transformer? [1 Mark]
(a) A step-up transformer has more number of turns in the secondary coil
(b) A step-down transformer increases the input voltage
(c) A step-down transformer has more number of turns in the primary coil
(d) A step-up transformer increases the input voltage

Answer: (b) A step-down transformer increases the input voltage

A step-down transformer decreases the input voltage, so statement (b) is incorrect.

Teacher's Note:
a) Step-down transformers have fewer turns in the secondary coil than in the primary coil.
b) Step-up transformers increase voltage while decreasing current.

14. The pressure inside a liquid [1 Mark]
(a) Increases with a decrease in the depth
(b) Increases with an increase in the depth
(c) Decreases with an increase in the depth
(d) Remains the same

Answer: (b) Increases with an increase in the depth

Liquid pressure is given by \( P = h d g \), which directly increases with depth \( h \).

Teacher's Note:
a) Pressure increases linearly with depth due to the weight of the liquid column above.
b) Depth is always measured from the free surface of the liquid.

15. Halley’s Comet was last seen in the year [1 Mark]
(a) 1984
(b) 1996
(c) 1986
(d) 1990

Answer: (c) 1986

Halley's Comet has a 76-year orbital period and was last visible from Earth in 1986.

Teacher's Note:
a) It is expected to return to the inner solar system around mid-2061.
b) It is the only known short-period comet that is regularly visible to the naked eye from Earth.

Question 2

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

Answer:

Teacher's Note:
a) A glass slab produces lateral displacement with parallel incident and emergent rays, making the angle of incidence equal to the angle of emergence.
b) Rubbing a glass rod with silk produces a positive static charge on the rod.

(B) Fill up the blanks and rewrite the sentences: [5 Marks]
1. A _________ image is formed by a convex lens only if the object is placed between the focus and the optical centre of the lens.
2. We measure liquid pressure using a ____________.
3. The direction of current can be detected using a ____________.
4. The curvy shape of a liquid near the point of contact is called the _________ of the liquid.
5. The splitting of heavy nuclei into small nuclei is called ___________.

Answer:
1. A virtual image is formed by a convex lens only if the object is placed between the focus and the optical centre of the lens.
2. We measure liquid pressure using a manometer.
3. The direction of current can be detected using a galvanometer.
4. The curvy shape of a liquid near the point of contact is called the meniscus of the liquid.
5. The splitting of heavy nuclei into small nuclei is called nuclear fission.

Teacher's Note:
a) Ensure correct scientific terminology is used for all blanks.
b) A manometer measures pressure differences, while a galvanometer detects small electric currents and their direction.

Question 3

(A) State whether the following statements are True or False. Correct the false statement and rewrite it. [5 Marks]
1. A conductor will not experience any force if the direction of the magnetic field is perpendicular to the direction of current.
2. The first satellite launched by the U.S.A. was the Explorer.
3. The permanent image on the film of a camera is called a photograph.
4. If the relative density of substance A is 0.85 and that of B is 1.15, then substance A is denser than water and B is lighter than water.
5. Thicker the wire, greater is its resistance.

Answer:
1. False. Correct statement: A conductor will not experience any force if the direction of the magnetic field is parallel to the direction of the current.
2. True.
3. False. Correct statement: The permanent image on the film of a camera is called a negative.
4. False. Correct statement: The relative density of substance A is less than water, and hence, it is lighter than water, whereas substance B having a higher relative density is denser than water.
5. False. Correct statement: Thicker the wire, lesser is its resistance.

Teacher's Note:
a) Magnetic force on a current-carrying conductor is maximum when perpendicular and zero when parallel to the field.
b) Resistance is inversely proportional to the cross-sectional area of the conductor.

(B) Give reasons for the following. [5 Marks]
1. Meteors are also known as shooting stars.
2. Cold drinks are efficiently cooled by ice pieces at \( 0^{\circ}\text{C} \).
3. All bodies immersed in a given fluid do not experience the same buoyant force.
4. An ebonite rod rubbed with fur becomes negatively charged.
5. A normal eye cannot clearly see an object kept closer than 25 cm.

Answer:
1. When meteors enter the Earth's atmosphere, they burn and evaporate due to the heat produced by friction. This makes the meteors luminous giving them the appearance of a star. Hence, meteors are also known as shooting stars.
2. Drinks are cooled more efficiently by ice pieces at \( 0^{\circ}\text{C} \) and not by water at \( 0^{\circ}\text{C} \) because \( 1\text{ g} \) of ice takes away \( 336\text{ J} \) of heat from the drink to melt into water at \( 0^{\circ}\text{C} \).
3. According to Archimedes' principle, bodies of different volumes will displace different weights of fluid. Hence, the buoyant force (equal to the weight of displaced fluid) on different objects will be different in a given fluid.
4. When an ebonite rod is rubbed with fur, the fur loses its electrons to the ebonite rod because the electrons in the outermost orbit of the fur are loosely bound as compared to those in the ebonite rod. This causes an excess of electrons in the ebonite rod and it becomes negatively charged.
5. The maximum accommodation of a normal human eye is reached when the object is at a distance of \( 25\text{ cm} \) from the eye. The focal length of the eye-lens cannot be decreased below this minimum limit. Thus, the eye is not able to see an object placed closer than \( 25\text{ cm} \).

Teacher's Note:
a) Emphasize latent heat of fusion of ice for cooling efficiency.
b) Buoyant force depends on the volume of the immersed body, not its weight or material.

Question 4

(A)

1. Why is Pluto not a classical planet? [3 Marks]

Answer:
A classical planet is a celestial body which:
(a) Orbits around the Sun.
(b) Has sufficient mass for its self gravity to pull it into a nearly spherical shape.
(c) Has a clear neighbourhood around its orbit.
Pluto fails to meet the third criterion as its oblong orbit overlaps the orbit of Neptune. Hence, it is no longer a classical planet and is now categorized as a dwarf planet.

Teacher's Note:
a) The IAU reclassified Pluto in August 2006.
b) Students must mention the clear neighbourhood condition to secure full marks.

2. How many calories are there in 2520 joules? [2 Marks]

Answer:
We know that \( 1\text{ calorie} = 4.2\text{ joules} \).
Hence, \( 1\text{ joule} = \frac{1}{4.2}\text{ calories} \).
Therefore, \( 2520\text{ joules} = \frac{2520}{4.2}\text{ calories} = 600\text{ calories} \).

Teacher's Note:
a) Always state the mechanical equivalent of heat (\( 1\text{ cal} = 4.2\text{ J} \)) explicitly.
b) Check the decimal division carefully during calculation.

(B)

1. Write the form of energy possessed by the body in the following situations: [2 Marks]
(a) A coconut falling from a tree
(b) An object raised to a certain height
(c) Wind blowing in an area
(d) A child driving a bicycle on a road

Answer:
(a) Kinetic as well as potential energy
(b) Potential energy
(c) Kinetic energy
(d) Kinetic energy

Teacher's Note:
a) A falling body possesses both gravitational potential energy and kinetic energy.
b) Moving air (wind) and moving bicycles possess kinetic energy.

2. Answer the following: [3 Marks]
(a) Mention the factors on which the direction of force experienced by a current carrying conductor, placed in a magnetic field, depends.
(b) Under what condition is the force experienced by a current carrying conductor placed in a magnetic field maximum?
(c) A proton beam is moving along the direction of a magnetic field. What force is acting on the proton beam?

Answer:
(a) Factors on which the direction of force depends are:
(i) The direction of current, and
(ii) The direction of the magnetic field.
(b) The force acting on a current-carrying conductor placed in a magnetic field is maximum when the direction of the current is at right angles (\( 90^{\circ} \)) to the direction of the magnetic field.
(c) As the proton beam moves parallel to the direction of the magnetic field, no force acts on it.

Teacher's Note:
a) Fleming's Left-Hand Rule governs the direction of this magnetic force.
b) Magnetic force is zero when the angle between current and magnetic field is \( 0^{\circ} \) or \( 180^{\circ} \).

Question 5

(A)

1. Can we recombine the seven spectral colors to obtain white light? Justify your answer. [2 Marks]

Answer:
Yes, we can recombine the seven colors. A prism splits white light into its seven constituent colours. When these colours fall on another identical prism placed in an inverted position with respect to the first, the colours recombine to form white light (Newton's recombination experiment).

[Figure: Two triangular prisms placed inversely; white light incident on the first prism splits into spectrum, and the inverted second prism recombines them back into white light.]

Teacher's Note:
a) This demonstrates that white light is a composite of seven colors.
b) Mentioning the inverted second prism is essential for complete credit.

2. Explain how surface tension plays a role in the following examples: [3 Marks]
(a) Insects walking on water
(b) Working of a tent
(c) Soaps and detergents

Answer:
(a) Insects walking on water: Small insects such as the water strider are able to walk on water because their weight is not enough to break the surface tension of the water, acting like a stretched elastic membrane.
(b) Working of tent: The material of a tent is waterproof as the surface tension of water bridges the pores in the finely woven material. However, when we touch the tent, the surface tension breaks and water seeps through.
(c) Soaps and detergents: Cleaning clothes becomes easier with soaps and detergents because they lower the surface tension of water, enabling it to soak into pores and soiled areas of the clothes.

Teacher's Note:
a) Surface tension arises due to cohesive forces between liquid molecules at the surface.
b) Surfactants (soaps) decrease surface tension to improve wetting ability.

(B)

1. Draw a labeled diagram of a gold leaf electroscope. Explain any one of its functions. [3 Marks]

Answer:
The labeled diagram of a gold leaf electroscope comprises a brass disc, insulator plug, brass rod, glass case, metal foil, and gold leaves.

[Figure: Gold leaf electroscope showing brass disc at top, insulating bush, vertical brass rod inside a glass jar, two thin gold leaves suspended at the bottom, and metal foil connected to earth.]

Function of a gold leaf electroscope:
Detection of a charge: The conductor is touched with the brass cap of the electroscope. If the conductor is charged, the gold leaves diverge due to similar charge repulsion. If the body is uncharged, the leaves show no divergence.

Teacher's Note:
a) An electroscope can also be used to test the nature of a charge (positive or negative).
b) Ensure all key parts like the brass cap, gold leaves, and earth connection are clearly labeled in the diagram.

2. A fan of power 300 W is used for 510 minutes. Calculate the electrical energy consumed in joules. [2 Marks]

Answer:
Given: Power \( P = 300\text{ W} = 0.3\text{ kW} \)
Time \( t = 510\text{ minutes} = \frac{510}{60}\text{ hours} = 8.5\text{ hours} \)
Energy consumed \( E = P \times t \)
\( E = 0.3\text{ kW} \times 8.5\text{ h} = 2.55\text{ kWh} \)
Since \( 1\text{ kWh} = 3.6 \times 10^{6}\text{ J} \):
\( E = 2.55 \times 3.6 \times 10^{6}\text{ J} = 9.18 \times 10^{6}\text{ J} \)

Teacher's Note:
a) Energy can also be calculated directly in joules as \( E = \text{Power (in watts)} \times \text{Time (in seconds)} \): \( 300 \times (510 \times 60) = 9.18 \times 10^{6}\text{ J} \).
b) Always double-check unit conversions for time and power.

Question 6

(A)

1. Define the following: [2 Marks]
(a) Focus of a concave lens
(b) Radius of curvature of a lens

Answer:
(a) Focus of a concave lens: For a concave lens, the rays of light incident parallel to the principal axis appear to diverge after refraction from a single point on the principal axis on the same side of the lens. This point is called the focus of the concave lens.
(b) Radius of curvature of a lens: It is the radius of the sphere of which the spherical surface of the lens forms a part.

Teacher's Note:
a) A concave lens has a virtual focus since rays only appear to diverge from it.
b) A lens has two surfaces, hence two radii of curvature corresponding to each spherical surface.

2. State the relation between the pressure and the depth h in a liquid of density d. What is the pressure at the bottom of a flask of height 40 cm containing water with density \( 1000\text{ kg m}^{-3} \)? [\( g = 9.8\text{ m s}^{-2} \)] [3 Marks]

Answer:
The relation between pressure \( P \) and depth \( h \) in a liquid of density \( d \) is:
\( P = h d g \)
Given: Height \( h = 40\text{ cm} = 0.4\text{ m} \), density \( d = 1000\text{ kg m}^{-3} \), acceleration due to gravity \( g = 9.8\text{ m s}^{-2} \).
Substituting the values:
\( P = 0.4 \times 1000 \times 9.8 = 3920\text{ N m}^{-2} \)

Teacher's Note:
a) Ensure all SI units are used consistently before calculation (\( \text{cm} \) must be converted to \( \text{m} \)).
b) The unit of pressure can be written as \( \text{N m}^{-2} \) or Pascals (\( \text{Pa} \)).

(B)

1. Find the odd one out giving reasons. [2 Marks]
(a) 1 light year, 1 year, 1 parsec, 1 kilometre
(b) Corona, Photosphere, Umbra, Core

Answer:
(a) 1 year: 1 year is a unit of time, whereas 1 light year, 1 parsec, and 1 kilometre are various units of distance.
(b) Umbra: Umbra is the dark shadow formed during an eclipse, whereas Corona, Photosphere, and Core are layers/regions of the Sun.

Teacher's Note:
a) Always state both the odd term and the common property of the remaining terms.
b) Light-year measures astronomical distances, not time.

2. What is Joule’s law of heating? An electric iron having resistance \( 100\text{ }\Omega \) works for 30 minutes when a current of \( 2\text{ A} \) flows through it. What is the heat produced by the iron? [3 Marks]

Answer:
Joule's law of heating states that the heat produced in a resistor is directly proportional to:
(a) the square of the current (\( I^{2} \)) flowing through it,
(b) the resistance (\( R \)) of the conductor, and
(c) the time (\( t \)) for which the current flows.
Formula: \( H = I^{2}Rt \)
Given: Resistance \( R = 100\text{ }\Omega \), Current \( I = 2\text{ A} \), Time \( t = 30\text{ minutes} = 30 \times 60 = 1800\text{ s} \).
Calculating heat produced:
\( H = (2)^{2} \times 100 \times 1800 = 4 \times 100 \times 1800 = 7,20,000\text{ J} = 7.2 \times 10^{5}\text{ J} \)

Teacher's Note:
a) Convert minutes to seconds before applying Joule's heating formula.
b) Express the final numerical answer in standard scientific notation.

Question 7

(A)

1. Write a short note on the human eye. [3 Marks]

Answer:
The human eye acts like a camera. Its lens system forms an inverted real image on the light-sensitive screen called the retina. Light enters the eye through a thin transparent membrane called the cornea. The iris controls the size of the pupil to regulate light entry. The ciliary muscles adjust the focal length of the eye-lens to view objects at various distances (power of accommodation). The least distance of distinct vision for a normal eye is \( 25\text{ cm} \).

Teacher's Note:
a) Mention key structures like cornea, iris, pupil, retina, and ciliary muscles.
b) Common defects include Myopia (shortsightedness) and Hypermetropia (longsightedness).

2. State the properties of magnetic lines of force. [2 Marks]

Answer:
Properties of magnetic lines of force (Any 4):
(1) Each line is a closed and continuous curve.
(2) They originate from the North Pole and terminate at the South Pole outside the magnet.
(3) Magnetic field lines never intersect each other.
(4) They are crowded near the poles where the magnetic field is strongest.
(5) They affect a magnetic compass needle.

Teacher's Note:
a) If two field lines intersected, it would mean two directions of the magnetic field at one point, which is impossible.
b) Always list at least four correct points for full credit in 2-mark questions.

(B)

1. A body of mass 200 g possesses 40 J of energy when placed at the top of a tower. How high is the tower? [\( g = 10\text{ m/s}^{2} \)] [2 Marks]

Answer:
Given: Potential Energy \( \text{PE} = 40\text{ J} \), mass \( m = 200\text{ g} = 0.2\text{ kg} \), \( g = 10\text{ m/s}^{2} \).
Formula: \( \text{PE} = m g h \)
\( h = \frac{\text{PE}}{m g} \)
\( h = \frac{40}{0.2 \times 10} = \frac{40}{2} = 20\text{ m} \)
Hence, the height of the tower is \( 20\text{ m} \).

Teacher's Note:
a) Convert grams to kilograms before substituting into the formula.
b) Gravitational potential energy depends on mass, acceleration due to gravity, and height.

2. What is the principle of floatation? How is it utilised in submarines? [3 Marks]

Answer:
Principle of floatation: A body floats in a liquid if the weight of the body is equal to the weight of the liquid displaced by it.
Working in submarines: A submarine has ballast tanks. When the submarine needs to submerge, these tanks are filled with sea water, making the total weight of the submarine greater than the weight of the water displaced, causing it to sink. When it needs to surface, compressed air empties the ballast tanks, making its weight less than the displaced water, causing it to float.

Teacher's Note:
a) State both the buoyancy condition and the weight-displacement relationship.
b) Ballast tanks control the overall average density of the submarine.