ICSE Class 8 Physics Sample Paper with Solutions Set 01

Question 1

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

1. The current which changes its direction after fixed intervals of time is called [1 Mark]
(a) Direct current
(b) Changing current
(c) Alternating current
(d) Varying current

Answer: (c) Alternating current

The current which changes its direction periodically after fixed intervals of time is known as alternating current or A.C.

Teacher's Note:
a) Direct current (D.C.) flows in one continuous direction, whereas alternating current (A.C.) reverses its direction periodically.
b) Students must remember that household supply is alternating current.

2. Where should we place an object in front of a convex lens to get a real image which is the same size as the object? [1 Mark]
(a) At the principal focus of the lens
(b) At twice the focal length
(c) At infinity
(d) Between the optical centre of the lens and its principal focus

Answer: (b) At twice the focal length

When an object is placed at \( 2F \) (twice the focal length) in front of a convex lens, a real, inverted image of the same size is formed at \( 2F \) on the other side.

Teacher's Note:
a) This is a standard property of lenses and mirrors similar to concave mirrors at the centre of curvature.
b) Do not confuse object position with focus, which forms an image at infinity.

3. What is the Indian name of the constellation 'Ursa Major'? [1 Mark]
(a) Vyadha
(b) Vrischika
(c) Simha
(d) Saptarishi

Answer: (d) Saptarishi

The well-known constellation Ursa Major, also known as the Great Bear, is called Saptarishi in Indian astronomy.

Teacher's Note:
a) 'Saptarishi' means a group of seven sages, referring to the seven prominent stars in the constellation.
b) Memorize traditional Indian names for major constellations as asked frequently in exams.

4. Potential energy is the energy possessed by an object due to its [1 Mark]
(a) Position
(b) Motion
(c) Speed
(d) Mass

Answer: (a) Position

Potential energy is the stored energy of position or configuration possessed by a body.

Teacher's Note:
a) Energy due to motion or speed is called kinetic energy.
b) Gravitational potential energy depends on the height and position of the object.

5. If the refractive index of two media are equal, then [1 Mark]
(a) Light will reflect in the same medium
(b) Interface will absorb the light
(c) No refraction will occur
(d) It will bend away from the normal

Answer: (c) No refraction will occur

Refraction occurs due to the change in speed of light when it passes from one medium to another with a different refractive index. If indices are equal, light passes straight without bending.

Teacher's Note:
a) Snell's law implies that if refractive indices are identical, the angle of incidence equals the angle of refraction.
b) Ensure students understand that bending requires an optical density difference.

6. The elevation in the central part of the retina of a human eye is called [1 Mark]
(a) Blind spot
(b) Yellow spot
(c) Fovea centralle
(d) Green spot

Answer: (b) Yellow spot

The yellow spot (macula lutea) is the central region of the retina responsible for sharp, clear central vision.

Teacher's Note:
a) The yellow spot has the maximum concentration of cone cells.
b) The blind spot is where the optic nerve leaves the eye and contains no photoreceptors.

7. The commercial unit of electric energy is [1 Mark]
(a) kilowatt-hour
(b) watt
(c) joule
(d) joule-hour

Answer: (a) kilowatt-hour

Electrical energy consumed in households and industries is commercially measured in kilowatt-hours (kWh), also known as a unit.

Teacher's Note:
a) One kilowatt-hour is equal to \( 3.6 \times 10^6 \) joules.
b) Watt is the unit of power, not energy.

8. The instrument used for measuring the density or relative density of liquids is known as [1 Mark]
(a) Spherometer
(b) Hydrometer
(c) Buoyancy meter
(d) Barometer

Answer: (b) Hydrometer

A hydrometer is a device based on Archimedes' principle used to measure the relative density of liquids.

Teacher's Note:
a) Barometer measures atmospheric pressure, and spherometer measures the radius of curvature of spherical surfaces.
b) Hydrometers sink deeper in liquids of lower density.

9. The loud sound heard during lightning is called [1 Mark]
(a) Lightning streak
(b) Cloud burst
(c) Thunder
(d) Sonic burst

Answer: (c) Thunder

Thunder is the booming or crashing sound caused by the rapid expansion of air heated by lightning.

Teacher's Note:
a) Light travels much faster than sound, which is why we see lightning before hearing thunder.
b) Be precise with meteorological definitions.

10. As we go higher into the atmosphere the density of air [1 Mark]
(a) Gradually increases
(b) Gradually decreases
(c) Remains the same throughout
(d) Initially decreases and then increases

Answer: (b) Gradually decreases

Atmospheric pressure and air density decrease with an increase in altitude because gravity pulls air molecules closer to the Earth's surface.

Teacher's Note:
a) Mountineers require oxygen cylinders due to decreased air density at high altitudes.
b) Memorize the vertical distribution characteristics of the atmosphere.

11. The temperature at which water vapourises into steam is called [1 Mark]
(a) Boiling point
(b) Melting point
(c) Freezing point
(d) Condensation temperature

Answer: (a) Boiling point

The boiling point of water is the specific temperature at which liquid water turns into steam at standard atmospheric pressure.

Teacher's Note:
a) For pure water at standard pressure, this temperature is \( 100^{\circ}\text{C} \).
b) Melting and freezing refer to solid-liquid transitions.

12. Surface tension has the dimensions of [1 Mark]
(a) Force
(b) Force per unit area
(c) Force per unit length
(d) Force \times length

Answer: (c) Force per unit length

Surface tension is defined as the force acting per unit length perpendicular to the line drawn on the surface of a liquid.

Teacher's Note:
a) Its SI unit is N/m.
b) Force per unit area defines pressure or stress.

13. In a uniform magnetic field, the field lines are [1 Mark]
(a) Curved
(b) Parallel equidistant straight lines
(c) Parallel but non-equidistant straight lines
(d) None of the above

Answer: (b) Parallel equidistant straight lines

A uniform magnetic field is represented by parallel and equally spaced straight field lines, indicating equal magnetic strength and direction.

Teacher's Note:
a) Non-uniform magnetic fields are represented by curved or non-equidistant lines.
b) The Earth's magnetic field in small regions can be treated as uniform.

14. How many constellations are officially recognised by the International Astronomical Union? [1 Mark]
(a) 76
(b) 88
(c) 108
(d) 95

Answer: (b) 88

The International Astronomical Union divides the celestial sphere into 88 official constellations.

Teacher's Note:
a) This standard division covers the entire night sky.
b) Facts like this require direct memorization.

15. The work done in moving a charge of 5 C across the potential difference of 10 V is [1 Mark]
(a) 50 J
(b) 2 J
(c) 0.5 J
(d) 25 J

Answer: (a) 50 J
Working:
\( W = Q \times V = 5\text{ C} \times 10\text{ V} = 50\text{ J} \)

Teacher's Note:
a) Use the formula Work = Charge \times Potential Difference (\( W = QV \)).
b) Ensure units are consistent in SI before multiplying.

Question 2

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

Answer:
1. Constellation - Vrischika
2. Prism - Dispersion
3. Microscope - Refraction
4. Camphor - Sublimation
5. Earth - Magnet

Teacher's Note:
a) Match items based on fundamental textbook definitions and applications.
b) Earth acts like a huge giant magnet with magnetic poles.

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

Answer:
1. A virtual image cannot be seen on a screen.
2. Coal, petroleum and natural gas are fossil fuels.
3. The iris controls and regulates the amount of light entering the eye.
4. The effect of a force acting vertically downwards on a unit area is called pressure.
5. In a series combination, the current is same across all the resistances.

Teacher's Note:
a) Real images can be caught on a screen, whereas virtual images cannot.
b) The iris acts like the diaphragm of a photographic camera.

Question 3

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

1. A rubber cork experiences the same upward thrust when immersed in oil and turpentine. [1 Mark]

Answer:
False. Different liquids have different densities, and hence, they exert a different upthrust. Therefore, a rubber cork experiences a different upthrust when immersed in oil and turpentine.

Teacher's Note:
a) Upthrust depends on the density of the liquid and the volume of the immersed object.
b) Always check fluid density when comparing buoyant forces.

2. Myopia is also called far-sightedness. [1 Mark]

Answer:
False. Myopia is also called near-sightedness.

Teacher's Note:
a) Myopia means short-sightedness where distant objects appear blurred.
b) Far-sightedness is termed hypermetropia.

3. Hydropower plants convert kinetic energy to electricity. [1 Mark]

Answer:
True.

Teacher's Note:
a) Flowing water possesses kinetic energy, which rotates turbines connected to generators.
b) Energy transformation questions require tracing the source from potential to kinetic to electrical.

4. The layer above the chronosphere is called the photosphere. [1 Mark]

Answer:
False. The layer above the chromosphere is called the corona (or the photosphere lies below the chromosphere).

Teacher's Note:
a) Order of solar atmosphere from inside out: Photosphere, Chromosphere, Corona.
b) Check layer sequences carefully in solar structure questions.

5. Tents do not remain water-proof when we touch them. [1 Mark]

Answer:
True.

Teacher's Note:
a) Touching canvas tents breaks the surface tension barrier, allowing water to leak through the fabric pores.
b) This is a classic application of surface tension in everyday life.

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

1. Stars appear to us like point objects. [1 Mark]

Answer:
The stars are much bigger than the Earth, yet they appear to us like point objects because they are millions of kilometres away from the Earth.

Teacher's Note:
a) Apparent size decreases drastically with immense distance.
b) Mention distance as the primary factor in your explanation.

2. A compass needle placed near a current carrying conductor shows deflection. [1 Mark]

Answer:
A current carrying conductor produces a magnetic field around it. Hence, a compass needle placed near the current carrying conductor shows deflection due to magnetic force.

Teacher's Note:
a) This demonstrates Oersted's discovery of the magnetic effect of electric current.
b) Compass needles respond exclusively to magnetic fields.

3. The snow on mountains does not melt as a whole. [1 Mark]

Answer:
The snow on mountains does not melt as a whole because of the high specific latent heat of fusion of ice. The snow melts gradually with the heat of the Sun.

Teacher's Note:
a) Ice requires a large amount of heat energy to phase-change into water at \( 0^{\circ}\text{C} \).
b) If latent heat were low, sudden melting would cause massive catastrophic floods.

4. Objects feel lighter when in water than outside it. [1 Mark]

Answer:
When we dip an object in water, an upward buoyant force acts on the object due to pressure difference between the top and bottom surfaces. This upward force reduces the apparent weight.

Teacher's Note:
a) Apparent weight equals true weight minus upthrust.
b) Cite Archimedes' principle in explanations.

5. A pool of water appears to be less deep than it actually is. [1 Mark]

Answer:
A pool of water appears to be less deep than it actually is because light rays coming from the bottom of the pool bend away from the normal as they pass from water into air.

Teacher's Note:
a) This is a consequence of refraction of light at the water-air boundary.
b) Mention virtual image formation due to refracted rays.

Question 4

(A)

1. Explain transfer of heat by conduction. [3 Marks]

Answer:
1. Conduction is the process by 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.
2. Conduction of heat energy takes place mainly in solids.
3. When a solid is heated from one end, its atoms gain heat energy and vibrate with greater amplitude about their mean positions, passing energy to neighboring atoms.

Teacher's Note:
a) Emphasize that there is no actual transfer or movement of matter in conduction.
b) Mention that solids are best conductors due to tightly packed atomic structures.

2. How do ciliary muscles affect the functioning of the eye? [2 Marks]

Answer:
1. Ciliary muscles can contract or relax to change the curvature and thickness of the eye lens.
2. This adjustment alters the focal length of the lens, enabling the eye to focus sharply on objects at varying distances (power of accommodation).

Teacher's Note:
a) Accommodation is vital for clear vision of both near and distant objects.
b) Weak ciliary muscles lead to vision defects requiring corrective lenses.

(B)

1. What energy transformations are taking place in the following examples? [2 Marks]
(a) Electric motor
(b) Burning of wood

Answer:
(a) Electric motor: Electrical energy is converted into mechanical energy.
(b) Burning of wood: Chemical energy is converted into heat energy and light energy.

Teacher's Note:
a) Clearly specify initial and final energy states.
b) Chemical energy is stored within molecular bonds.

2. Answer the following: [3 Marks]
(a) Define: Valence electrons.
(b) When can you say that an atom becomes negatively charged?
(c) When can you say that an atom becomes positively charged?

Answer:
(a) Valence electrons are the electrons present in the outermost orbit of an atom.
(b) An atom becomes negatively charged when it gains electrons, making the number of electrons exceed protons.
(c) An atom becomes positively charged when it loses electrons, making protons exceed electrons.

Teacher's Note:
a) Electron transfer dictates ionic charge states.
b) Protons remain locked in the nucleus and do not participate in ionization.

Question 5

(A)

1. Define the following: [2 Marks]
(a) Optical Centre
(b) Principal Axis

Answer:
(a) Optical centre: It is the geometrical centre of a lens through which a ray of light passes without any deviation.
(b) Principal axis: It is the straight line passing through the optical centre of the lens and perpendicular to both its spherical faces.

Teacher's Note:
a) Light passing through the optical centre suffers zero net lateral displacement.
b) The principal axis serves as the reference line for measuring focal lengths.

2. Describe the Milky Way galaxy. [3 Marks]

Answer:
1. Our solar system belongs to the Milky Way galaxy, known in Indian astronomy as Akash Ganga.
2. It is a spiral galaxy featuring spiral arms emerging from a dense central nucleus.
3. From Earth, we view it edge-on as a bright band across the night sky, extending about \( 1,00,000 \) light years across.

Teacher's Note:
a) Mention both scientific and traditional names.
b) State structural features like spiral arms and dimensions clearly.

(B)

1. Answer the following: [3 Marks]
(a) What are magnetic field lines?
(b) Draw field lines when two bar magnets are placed with their like poles facing each other.
(c) List any two properties of magnetic field lines.

Answer:
(a) A magnetic field line is an imaginary continuous curve along which a hypothetical free North pole tends to move.
(b) [Figure: Two bar magnets with North poles facing each other, showing diverging field lines that bend away from each other with a neutral point in between where field lines do not cross.]
(c) 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) Like poles repel, resulting in divergent field lines with zero magnetic induction at the neutral point.
b) Intersection would imply two directions of magnetic force at a single point, which is physically impossible.

2. Two coils 1 and 2 of insulated copper wire having large but different number of turns are wound over a cardboard cylinder. Coil 1 is connected to battery and a plug key. Coil 2 is connected to a galvanometer. How will the galvanometer reading change when [3 Marks]
(a) key is plugged in?
(b) key is taken out?
Give reasons for your answers.

Answer:
(a) When the key is plugged in: The galvanometer shows a momentary deflection in one direction because current rises from zero to maximum, changing the magnetic flux linked with coil 2.
(b) When the key is taken out: The galvanometer shows a momentary deflection in the opposite direction because current falls from maximum to zero, collapsing the magnetic field around coil 2.

Teacher's Note:
a) This illustrates electromagnetic induction due to changing magnetic flux.
b) Steady current produces no deflection; only changing current induces electromotive force (emf).

Question 6

(A)

1. Why do different colours of light deviate differently in a prism? [2 Marks]

Answer:
1. Different colours of light have different wavelengths.
2. Consequently, they travel at different speeds in a transparent medium like glass or water, causing them to refract or bend through different angles.

Teacher's Note:
a) Violet light has the shortest wavelength and bends the most.
b) Red light has the longest wavelength and bends the least.

2. Draw a ray diagram to show the formation of an image, when the object is placed between the optical centre and the principal focus of a convex lens. [3 Marks]

Answer:
[Figure: Ray diagram showing a convex lens with optical centre O, principal focus F₁ and F₂. An object AB is placed between O and F₁. A ray parallel to the principal axis passes through F₂. A second ray passing through O goes straight without deviation. Backwards extension of these divergent rays produces an enlarged, virtual, erect image A'B' on the same side of the lens as the object.]

Teacher's Note:
a) Ensure arrows are marked properly on all incident and refracted rays.
b) This setup is used as a magnifying glass.

(B)

1. A rectangular block of dimensions 25 cm, 25 cm, 15 cm weighs 25 N. What will be the pressure exerted by its largest face on the surface? [2 Marks]

Answer:
Working:
Dimensions of the block: \( 25\text{ cm} \times 25\text{ cm} \times 15\text{ cm} \).
Area of the largest face (\( A \)) = \( 25\text{ cm} \times 25\text{ cm} = 625\text{ cm}^2 = 0.0625\text{ m}^2 \).
Force (\( F \)) = weight = \( 25\text{ N} \).
Pressure (\( P \)) = \( \frac{F}{A} = \frac{25}{0.0625} = 400\text{ N/m}^2 = 400\text{ Pa} \).

Teacher's Note:
a) Always convert dimensions from centimeters to meters before calculating pressure in Pascals.
b) Pressure is inversely proportional to area for a given force.

2. Find the equivalent resistance when three resistances of \( 3\ \Omega \), \( 6\ \Omega \) and \( 9\ \Omega \) are connected in: [3 Marks]
(a) Series
(b) Parallel

Answer:
Given resistances: \( R_1 = 3\ \Omega \), \( R_2 = 6\ \Omega \), \( R_3 = 9\ \Omega \).
(a) For a series connection:
\( R_s = R_1 + R_2 + R_3 = 3 + 6 + 9 = 18\ \Omega \)
(b) For a parallel connection:
\( \frac{1}{R_p} = \frac{1}{R_1} + \frac{1}{R_2} + \frac{1}{R_3} \)
\( \frac{1}{R_p} = \frac{1}{3} + \frac{1}{6} + \frac{1}{9} = \frac{6 + 3 + 2}{18} = \frac{11}{18} \)
\( R_p = \frac{18}{11} = 1.67\ \Omega \)

Teacher's Note:
a) Equivalent resistance in series is always greater than the largest individual resistance.
b) Equivalent resistance in parallel is always smaller than the smallest individual resistance.

Question 7

(A)

1. Answer the following: [3 Marks]
(a) What is heat?
(b) Describe sea breeze.

Answer:
(a) Heat is a form of energy that produces the sensation of hotness or coldness in a body.
(b) Sea breeze: During the day, land heats up faster than water due to lower specific heat capacity of sand. The hot air above land rises, and cooler air from the sea flows towards the land, creating a sea breeze.

Teacher's Note:
a) Heat flows naturally from a body at higher temperature to a body at lower temperature.
b) Sea breeze occurs during daytime; land breeze occurs at night.

2. Find out the quantity of heat produced in a resistance of \( 10\ \Omega \) when a current of 2 A is supplied to it for 8 minutes. [2 Marks]

Answer:
Working:
Given: Resistance (\( R \)) = \( 10\ \Omega \), Current (\( I \)) = \( 2\text{ A} \), Time (\( t \)) = \( 8\text{ minutes} = 8 \times 60 = 480\text{ seconds} \).
Using Joule's law of heating (\( H = I^2Rt \)):
\( H = (2)^2 \times 10 \times 480 \)
\( H = 4 \times 10 \times 480 = 19,200\text{ J} \)

Teacher's Note:
a) Always convert time from minutes to seconds before calculating heat energy in Joules.
b) Ensure proper substitution in Joule's heating formula.

(B)

1. What is the distance of a star in light years, if it is at a distance of 20 parsec? [2 Marks]

Answer:
Working:
Given: \( 1\text{ parsec} = 3.26\text{ light years} \).
Distance = \( 20 \times 3.26 = 65.2\text{ light years} \).

Teacher's Note:
a) Parsec and light years are astronomical units of distance.
b) One parsec equals approximately \( 3.26 \) light years.

2. What is meant by the relative density of a substance? What is its significance? The relative density of mercury is 13.6. What is its density in S.I. units? (Density of water = \( 1000\text{ kg/m}^3 \)) [3 Marks]

Answer:
1. Relative density of a substance is defined as the ratio of the density of the substance to the density of water at \( 4^{\circ}\text{C} \).
2. Significance: Relative density indicates how heavy a substance is compared to an equal volume of water.
3. Calculation for mercury:
\( \text{Density of mercury} = \text{Relative Density} \times \text{Density of water} \)
\( \text{Density} = 13.6 \times 1000\text{ kg/m}^3 = 1.36 \times 10^4\text{ kg/m}^3 \) (or \( 13,600\text{ kg/m}^3 \)).

Teacher's Note:
a) Relative density is a dimensionless quantity having no units.
b) Multiply relative density by \( 1000\text{ kg/m}^3 \) to convert to SI density units.