ICSE Class 8 Physics Sample Paper with Solutions Set 05

Question 1

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

1. If the number of turns in a solenoid is increased, the strength of the magnetic field produced will [1 Mark]
(a) Decrease
(b) Remain the same
(c) Increase
(d) Increase first and then decrease

Answer: (c) Increase

The magnetic field strength inside a solenoid is directly proportional to the number of turns per unit length.

Teacher's Note:
a) Recall that increasing the number of turns increases the total magnetic field produced.
b) Students often confuse the density of turns with core material properties.

2. Buoyant force exerted by a fluid on a body is equal to the [1 Mark]
(a) Mass of the body
(b) Weight of the body
(c) Apparent loss of weight of the body
(d) None of these

Answer: (c) Apparent loss of weight of the body

According to Archimedes principle, the upward buoyant force equals the weight of the displaced fluid, which manifests as the apparent loss of weight.

Teacher's Note:
a) Note that buoyant force equals the weight of displaced liquid, measured as apparent loss of weight.
b) Do not mistake it for the total weight of the floating body unless the body is floating in equilibrium.

3. Lightning is caused in the sky due to [1 Mark]
(a) Two oppositively charged clouds
(b) Two similarly charged clouds
(c) One neutral and one charged cloud
(d) None of these

Answer: (a) Two oppositively charged clouds

Massive static electric discharge occurs between clouds carrying opposite charges.

Teacher's Note:
a) Understand that friction between air molecules and water droplets charges the clouds.
b) Watch for spelling variants in exam choices such as oppositively.

4. The specific heat of water is [1 Mark]
(a) 42000 Jkg^-1C^-1
(b) 4200 Jkg^-1C^-1
(c) 420 Jkg^-1C^-1
(d) 4250 Jkg^-1C^-1

Answer: (b) 4200 Jkg^-1C^-1

Water has a high specific heat capacity of approximately \( 4200\text{ J kg}^{-1}\text{}^{\circ}\text{C}^{-1} \).

Teacher's Note:
a) Memorize standard physical constants like the specific heat of water.
b) Pay close attention to powers of ten in the options.

5. A ray of light going from an optically rarer medium to an optically denser medium [1 Mark]
(a) Remains undeviated
(b) Bends towards the normal
(c) Bends away from the normal
(d) None of these

Answer: (b) Bends towards the normal

When light enters a denser medium, its speed decreases, causing it to bend towards the normal.

Teacher's Note:
a) Rule: Rarer to denser bends towards normal; denser to rarer bends away.
b) Students frequently invert rarer and denser conditions.

6. Time taken by light to reach the Earth from the Sun is [1 Mark]
(a) 18 minutes and 10 seconds
(b) 8 minutes and 10 seconds
(c) 10 minutes and 16 seconds
(d) 16 minutes and 10 seconds

Answer: (b) 8 minutes and 10 seconds

Light takes approximately 500 seconds (roughly 8 minutes and 20 seconds, or 8 minutes 10 seconds as standard textbook data) to travel from the Sun to Earth.

Teacher's Note:
a) Distance is about 1.50 \times 10⁸ km, divided by speed 3 \times 10⁸ m/s.
b) Accept standard rounded textbook values.

7. Which of these is a renewable source of energy? [1 Mark]
(a) Coal
(b) Petroleum
(c) Solar energy
(d) L.P.G

Answer: (c) Solar energy

Solar energy is inexhaustible and continuously replenished by the Sun.

Teacher's Note:
a) Distinguish between fossil fuels (non-renewable) and natural perpetual flows (renewable).
b) LPG, coal, and petroleum take millions of years to form.

8. The direction of magnetic lines of force due to a current carrying straight conductor when the electric current flows upwards is [1 Mark]
(a) Clockwise
(b) Anticlockwise
(c) Upwards
(d) Downwards

Answer: (b) Anticlockwise

Applying the right hand thumb rule with the thumb pointing upwards, the fingers curl in an anticlockwise direction.

Teacher's Note:
a) Always use the right hand thumb rule for straight current-carrying conductors.
b) Reversing the current direction reverses the magnetic field direction.

9. For a person suffering from hypermetropia, the image of a nearby object is focused ____________ the retina. [1 Mark]
(a) Behind
(b) In front of
(c) On
(d) None of these

Answer: (a) Behind

In hypermetropia (farsightedness), light rays converge behind the retina.

Teacher's Note:
a) Myopia focuses in front; hypermetropia focuses behind.
b) Correct hypermetropia using a convex lens.

10. Sea breeze occurs due to a fall in pressure over the surface of [1 Mark]
(a) Air
(b) Water
(c) Land
(d) Sea

Answer: (c) Land

During the day, land heats up faster than the sea, creating low pressure over the land, which draws cooler air from the sea.

Teacher's Note:
a) Winds blow from high pressure (sea) to low pressure (land) during a sea breeze.
b) Land breeze occurs at night when land cools down faster.

11. The atmospheric pressure at sea level is [1 Mark]
(a) 76 cm of mercury column
(b) 70 cm of mercury column
(c) 80 cm of mercury column
(d) 66 cm of mercury column

Answer: (a) 76 cm of mercury column

Standard atmospheric pressure supports a mercury column of 76 cm (or 760 mm).

Teacher's Note:
a) 76 cm of Hg is equivalent to 1.013 \times 10⁵ Pa.
b) Barometers measure this pressure using mercury.

12. When light is dispersed by a prism, the colour least dispersed is [1 Mark]
(a) Violet
(b) Indigo
(c) Yellow
(d) Red

Answer: (d) Red

Red light has the longest wavelength and lowest refractive index in glass, hence it deviates the least.

Teacher's Note:
a) Order of deviation: Red deviates the least, violet the most.
b) Remember the acronym VIBGYOR for increasing wavelength and decreasing deviation.

13. The direction of conventional current is from [1 Mark]
(a) Higher potential to lower potential
(b) Lower potential to higher potential
(c) Both a and b
(d) None of the above

Answer: (a) Higher potential to lower potential

Conventional current flows by convention from the positive terminal (higher potential) to the negative terminal (lower potential).

Teacher's Note:
a) Electron flow is opposite, from lower to higher potential.
b) Always distinguish between electronic current and conventional current.

14. Earth behaves like a huge bar magnet with its Magnetic North Pole situated near the [1 Mark]
(a) Geographical South Pole
(b) Geographical North Pole
(c) Geographical East Pole
(d) Geographical West Pole

Answer: (a) Geographical South Pole

The Earth's magnetic field lines emerge near the geographic southern hemisphere, meaning the magnetic north pole is located near the geographic south pole.

Teacher's Note:
a) The north pole of a compass needle points towards the geographic north, which is magnetically a south pole.
b) This is a classic conceptual trick in magnetism.

15. Which of these is not obtained from petroleum? [1 Mark]
(a) Diesel
(b) CNG
(c) Biogas
(d) Kerosene

Answer: (c) Biogas

Biogas is produced by the anaerobic decomposition of organic matter, whereas diesel, CNG, and kerosene are derived from petroleum or natural gas fractions.

Teacher's Note:
a) Fractional distillation of petroleum yields diesel, petrol, kerosene, and paraffin wax.
b) CNG is compressed natural gas, often found alongside petroleum deposits, but biogas is biological.

Question 2

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

Answer:
1. Latent heat of fusion of ice - 336000 J/kg (336 J/g)
2. Like charges - Repulsion
3. Velocity of light - 3 \times 10⁸ m/s
4. Artificial satellite - Aryabhatta
5. Rainbow - Dispersion

Teacher's Note:
a) Match physical terms with their correct standard values or phenomena.
b) Check unit consistency carefully when reading latent heat values.

(B) Fill up the blanks and rewrite the sentences: [5 Marks]

1. Steam from within the Earth can be used to generate electricity. This is called ___________ energy. [1 Mark]

Answer: geothermal

Teacher's Note:
a) Geo means earth, thermal means heat.
b) It is a renewable source of energy tapped from underground steam reservoirs.

2. In a step up transformer, the ___________ coil is thicker; less heavily insulated and has less number of turns. [1 Mark]

Answer: primary

Teacher's Note:
a) A step-up transformer increases voltage, meaning secondary has more turns and thinner wire.
b) Therefore, the primary coil has fewer turns and thicker wire.

3. The pressure exerted by a solid is directly proportional to its ___________ and inversely proportional to its ___________. [1 Mark]

Answer: weight (or thrust), surface area

Teacher's Note:
a) Formula: Pressure = Force / Area.
b) Greater force increases pressure, greater area decreases pressure.

4. When an ebonite rod is rubbed with fur, the charge acquired by the ebonite rod is ___________. [1 Mark]

Answer: negative

Teacher's Note:
a) Triboelectric series dictates that ebonite gains electrons from fur.
b) Gaining electrons results in a negative charge.

5. Between air and water, ___________ is the denser medium. [1 Mark]

Answer: water

Teacher's Note:
a) Optical and mass density of liquid water is greater than that of air.
b) Light slows down more in water than in air.

Question 3

(A) State whether the following statements are True or False. Correct the false statement and rewrite it. [5 Marks]

1. The distance between the focus and optical centre of a lens is called its focal length. [1 Mark]

Answer: True.

Teacher's Note:
a) Focal length is measured from the optical centre to the principal focus.
b) This is a standard definition in optics.

2. An electromagnet is a permanent magnet. [1 Mark]

Answer: False. An electromagnet is a temporary magnet.

Teacher's Note:
a) Electromagnets require electric current to maintain their magnetic field.
b) Once current stops, they lose magnetism.

3. Human body is a good conductor of electricity. [1 Mark]

Answer: True.

Teacher's Note:
a) Body fluids contain dissolved ions that conduct electric current.
b) Hence precautions are necessary around high-voltage equipment.

4. Atmospheric pressure decreases as we move from sea level to higher altitudes. [1 Mark]

Answer: True.

Teacher's Note:
a) Air column above decreases at higher altitudes, leading to lower pressure.
b) This causes mountaineers to experience breathing difficulties.

5. Evaporation needs an external source of heat. [1 Mark]

Answer: False. Evaporation does not need an external source of heat (it can take place at any temperature using internal thermal energy).

Teacher's Note:
a) Evaporation happens at all temperatures by absorbing latent heat from the liquid itself or surroundings.
b) Boiling requires a specific external heat source at a fixed temperature.

(B) Give reasons for the following. [5 Marks]

1. A concave lens is used in spectacles for the correction of myopia. [1 Mark]

Answer: A concave lens is a diverging lens that diverges incoming light rays before they enter the eye, enabling the image of a distant object to be focused directly on the retina.

Teacher's Note:
a) Myopia causes light to focus in front of the retina.
b) A concave lens pushes the focal point back onto the retina.

2. The Sun appears to move from the east to the west. [1 Mark]

Answer: The Earth rotates on its axis from west to east, which causes the apparent daily motion of the Sun from east to west.

Teacher's Note:
a) This is an apparent motion caused by Earth's rotation.
b) Similar to trees appearing to move backward from a moving train.

3. A comb rubbed on dry hair attracts small bits of paper. [1 Mark]

Answer: Rubbing a comb on dry hair charges it by friction; the charged comb induces an opposite charge on neutral bits of paper, causing attraction.

Teacher's Note:
a) Static electricity causes induction in neutral objects.
b) Charged objects attract uncharged light objects due to electrostatic force.

4. Water has a tendency to form spherical droplets. [1 Mark]

Answer: Due to surface tension, molecules of water experience inward cohesive forces, causing the liquid surface to contract and acquire the minimum possible surface area for a given volume, which is a sphere.

Teacher's Note:
a) Surface tension minimizes surface area.
b) A sphere has the minimum surface area for a given volume.

5. An ice-cube is used for cooling a drink. [1 Mark]

Answer: Ice absorbs its latent heat of fusion (336 J/g) from the drink to melt at 0 degrees Celsius, thereby extracting a large amount of thermal energy and cooling the drink effectively.

Teacher's Note:
a) Phase change from solid to liquid absorbs substantial heat without changing temperature.
b) Ice cools drinks much more efficiently than cold water at 0 degrees Celsius for this reason.

Question 4

(A)

1. What is an electromagnet? How is it different from a permanent magnet? State any two uses of an electromagnet. [3 Marks]

Answer:
1. Definition: A temporary magnet made by placing a soft iron core inside a current-carrying solenoid.
2. Difference: An electromagnet has adjustable magnetic strength and its polarity can be reversed by reversing the current, whereas a permanent magnet has fixed polarity and constant strength.
3. Uses: Used in electric bells and cranes for lifting heavy iron scrap.

Teacher's Note:
a) Emphasize that soft iron loses magnetism quickly when current stops.
b) Permanent magnets are typically made of steel or alnico.

2. State the laws of refraction of light. [2 Marks]

Answer:
1. First law: The incident ray, the refracted ray, and the normal to the interface at the point of incidence all lie in the same plane.
2. Second law (Snell's Law): The ratio of the sine of the angle of incidence to the sine of the angle of refraction is constant for a given pair of media (\( \frac{\sin i}{\sin r} = \mu \)).

Teacher's Note:
a) State both laws clearly with mathematical expression for Snell's law.
b) Mention that the constant \( \mu \) is the refractive index.

(B)

1. Why are astronauts made to wear special suits? [2 Marks]

Answer:
1. Atmospheric pressure is extremely low or negligible in space, which would cause bodily fluids to boil or expand dangerously.
2. Special suits maintain an internal pressure matching normal atmospheric pressure and protect astronauts from extreme temperatures and radiation.

Teacher's Note:
a) Highlight the danger of zero atmospheric pressure on human fluids.
b) Suits provide artificial life support and pressure compensation.

2. Give three observations in our daily life where the principle of evaporation produces cooling. [3 Marks]

Answer:
1. We feel cool under a ceiling fan after perspiring because the airflow accelerates the evaporation of sweat.
2. Water kept in an earthen pot (matka) stays cool due to evaporation through microscopic pores in the clay.
3. A desert cooler blows cool air because water evaporating from its pads absorbs heat from the surrounding air.

Teacher's Note:
a) Explain that evaporation absorbs latent heat from surroundings.
b) Give concrete, everyday examples as required.

Question 5

(A)

1. What is nuclear energy? State two precautions to be taken care in nuclear power plants. [2 Marks]

Answer:
1. Nuclear energy is the energy released during nuclear reactions, such as nuclear fission or fusion, involving changes in the atomic nucleus.
2. Precautions: Proper disposal mechanisms for radioactive waste, and housing reactors inside thick lead-walled containment structures.

Teacher's Note:
a) Define nuclear energy in terms of mass-energy equivalence or nuclear reactions.
b) Emphasize safety measures against radiation leakage.

2. State two differences between charging by conduction and charging by induction. [3 Marks]

Answer:
1. Contact: Conduction requires physical contact between the charged and uncharged body, whereas induction requires no physical contact.
2. Charge transfer: In conduction, actual charge flows from one body to the other; in induction, charges are redistributed within the body without direct transfer from the inductor.
3. Loss of charge: Some charge is lost during conduction due to transfer, whereas no charge is lost by the inducing body in induction.

Teacher's Note:
a) Clearly distinguish physical contact versus electrostatic induction.
b) Mention charge conservation and loss aspects.

(B)

1. State the right hand thumb rule to find the direction of the magnetic field around a current-carrying straight conductor. Illustrate using a diagram. [3 Marks]

Answer:
1. Rule: Hold a current-carrying straight conductor in your right hand such that your thumb points in the direction of the electric current. Your fingers will wrap around the conductor in the direction of the magnetic field lines.
2. [Figure: Diagram showing a right hand grasping a vertical red wire with thumb pointing upwards representing current, and concentric blue circular arrows representing magnetic field lines]

Teacher's Note:
a) Describe the rule precisely mentioning the right hand.
b) Mention how thumb and curled fingers correspond to current and magnetic field respectively.

2. State the law of floatation. Why does ice float on the surface of water? [2 Marks]

Answer:
1. Law of floatation: A floating body displaces a weight of fluid equal to its own total weight.
2. Reason: Ice floats because its density (\( 0.92\text{ g/cm}^3 \)) is less than the density of liquid water (\( 1.0\text{ g/cm}^3 \)), allowing it to experience an upward upthrust equal to its weight while being only partially submerged.

Teacher's Note:
a) State the balance between weight and buoyant force.
b) Compare densities clearly to explain ice floating.

Question 6

(A)

1. Complete the diagram in your answer book and write the nature of the image formed. [2 Marks]

Answer:
1. [Figure: Convex lens ray diagram with object placed between F1 and optical centre O, showing virtual rays extending backward to form an enlarged upright image on the same side as the object]
2. Nature of the image formed: Virtual, erect, and magnified (enlarged).

Teacher's Note:
a) Recognize the special case of a convex lens where the object is within the focal length.
b) State all three characteristics: virtual, erect, and enlarged.

2. State Archimedes’ principle. The following figure shows three identical blocks of wood floating in three different liquids A, B and C of densities d1, d2 and d3 respectively. Which of these has the highest density? Give reasons to justify your answer. [3 Marks]

[Figure: Three rectangular containers A, B, and C showing identical wooden blocks floating with different immersion depths. Container A has the deepest immersion, B intermediate, and C the least immersion, labeled with liquid densities d1, d2, and d3 respectively.]

Answer:
1. Archimedes' principle: When an object is wholly or partially immersed in a fluid, it experiences an upward buoyant force (upthrust) equal to the weight of the fluid displaced by it.
2. Liquid C has the highest density (\( d_3 \)).
3. Reason: Since the wooden blocks are identical, they experience the same weight and therefore displace the same weight of liquid. A denser liquid exerts greater upthrust for a smaller volume of immersion, meaning the block sinks least in the liquid with the highest density.

Teacher's Note:
a) Connect immersion depth with liquid density.
b) Less immersion volume implies higher liquid density for the same weight of floating body.

(B)

1. Define specific latent heat of fusion. Calculate the specific latent heat of fusion of ice when 200 g at 0 degrees Celsius is converted to water by supplying 67200 J of heat. [2 Marks]

Answer:
1. Definition: Specific latent heat of fusion is the amount of heat energy required to convert unit mass (\( 1\text{ kg} \) or \( 1\text{ g} \)) of a solid into liquid at its melting point without any change in temperature.
2. Calculation:
\( Q = 67200\text{ J} \)
\( m = 200\text{ g} \)
\( L = \frac{Q}{m} = \frac{67200}{200} = 336\text{ J/g} \) (or \( 336000\text{ J/kg} \)).

Teacher's Note:
a) Formula: \( L = \frac{Q}{m} \).
b) Include correct units in the final answer (J/g or J/kg).

2. Differentiate between the following: [3 Marks]
(a) Concave and convex lens
(b) Solids and liquids

Answer:

Teacher's Note:
a) Use tabular format for clear differentiation.
b) Cover optical properties for lenses and molecular properties for states of matter.

Question 7

(A)

1. Distinguish between galaxy and constellation. On which day does a lunar eclipse always occur? [3 Marks]

Answer:

Lunar eclipse occurrence: A lunar eclipse always occurs on a full moon day.

Teacher's Note:
a) Distinguish galactic scales from star patterns (constellations).
b) Remember that lunar eclipses happen during full moon when Earth is between Sun and Moon.

2. State any three assumptions of the kinetic theory. [2 Marks]

Answer:
1. Matter is made up of tiny particles (atoms or molecules) which are in a state of continuous random motion.
2. The kinetic energy of these molecules increases with an increase in temperature and decreases with a decrease in temperature.
3. Molecules exert intermolecular forces of attraction on one another (cohesive forces between similar molecules, adhesive forces between dissimilar molecules).

Teacher's Note:
a) State fundamental postulates of kinetic molecular theory clearly.
b) Mention molecular motion and temperature dependence.

(B)

1. State any four precautions which one should take while using energy in everyday life. [2 Marks]

Answer:
1. Switch off lights, fans, and electrical appliances when not in use.
2. Use energy-efficient appliances such as LED bulbs and 5-star rated equipment.
3. Prefer public transport, carpooling, or walking instead of personal vehicles to save fossil fuels.
4. Maximize the use of renewable energy sources like solar power wherever possible.

Teacher's Note:
a) Focus on energy conservation practices.
b) List practical, everyday habits.

2. How do you charge a body by induction? Explain with the help of an example. [3 Marks]

Answer:
1. Charging by induction is the process of charging an uncharged conductor by bringing a charged body close to it without making physical contact.
2. Example explanation: When a positively charged glass rod (B) is brought near an uncharged isolated metallic conductor (A) mounted on an insulating stand, free electrons in A are attracted towards B. Consequently, the near end of A acquires a negative charge and the farther end acquires an equal positive charge due to electron deficiency.

[Figure: Diagram showing an uncharged metal conductor A on an insulating stand, with a positively charged rod B brought near its right end, showing negative charges accumulated on the near end and positive charges on the far end]

Teacher's Note:
a) Emphasize that no direct physical contact occurs during induction.
b) Explain redistribution of charges (opposite charge on near end, like charge on far end).