ICSE Class 7 Physics Sample Paper with Solutions Set 04

1. The pendulum of a clock has: [1 Mark]
(a) Periodic motion
(b) Circular Motion
(c) Rectilinear Motion
(d) All of the above

Answer: (A) Periodic motion

The pendulum of a clock repeats its motion in equal intervals of time, which is periodic motion.

Teacher's Note:
a) Periodic motion is defined as a motion that repeats itself at regular intervals of time.
b) Students often confuse periodic motion with oscillatory motion; while all oscillatory motions are periodic, not all periodic motions are oscillatory.

2. 1 tonne is equal to [1 Mark]
(a) 100 quintal
(b) 1000 quintal
(c) 10 quintal
(d) 100000 quintal

Answer: (C) 10 quintal

1 tonne = 1000 kg and 1 quintal = 100 kg, therefore 1 tonne = 10 quintals.

Teacher's Note:
a) Conversion units of mass must be memorized thoroughly by students to avoid calculation errors.
b) Note that 1 tonne equals 1,000 kg, whereas 1 quintal equals 100 kg.

3. Plastic covering on electric wires provides [1 Mark]
(a) Good looks
(b) Insulation
(c) Good connection
(d) Colour distinction

Answer: (B) Insulation

Plastic is a poor conductor of electricity and acts as an insulator to prevent electric shocks.

Teacher's Note:
a) Insulators are materials that do not allow electric current to pass through them easily.
b) Plastic and rubber are commonly used as covering materials for electrical wires and tools for safety.

4. Which waves are employed in SONAR? [1 Mark]
(a) X-rays
(b) Infrasonic Wave
(c) Ultrasonic Wave
(d) SONAR wave

Answer: (C) Ultrasonic Wave

SONAR (Sound Navigation and Ranging) uses ultrasonic waves to measure distances and detect underwater objects.

Teacher's Note:
a) Ultrasonic waves have frequencies greater than \( 20,000\text{ Hz} \), making them ideal for navigating and ranging under water.
b) Do not confuse SONAR with RADAR, which uses radio waves.

5. How does the alphabet M look in a pinhole camera? [1 Mark]
(a) W
(b) M
(c) Both possible
(d) None

Answer: (A) W

A pinhole camera forms an inverted image, causing the top and bottom of the object to reverse, so 'M' appears as 'W'.

Teacher's Note:
a) The image formed by a pinhole camera is always real and inverted.
b) Inversion causes vertical flipping, transforming upright features into upside-down features.

6. The device used to measure temperature is called [1 Mark]
(a) Scale
(b) Pressure gauge
(c) Thermometer
(d) Barometer

Answer: (C) Thermometer

A thermometer is a device specifically designed to measure temperature.

Teacher's Note:
a) Barometers measure atmospheric pressure, while thermometers measure thermal degree or temperature.
b) Mercury and alcohol are commonly used liquids inside laboratory and clinical thermometers.

7. A ray of light travelling parallel to the principle axis after reflection from a concave mirror passes through the [1 Mark]
(a) Focus
(b) Center of curvature
(c) Pole
(d) None of these

Answer: (A) Focus

By definition, light rays parallel to the principal axis converge at the principal focus after reflection from a concave mirror.

Teacher's Note:
a) This is one of the standard principal ray rules used in ray diagrams for spherical mirrors.
b) Students must remember that rays passing through the focus become parallel to the principal axis after reflection.

8. Rate of distance travelled with time is termed as [1 Mark]
(a) Displacement
(b) Acceleration
(c) Velocity
(d) Speed

Answer: (D) Speed

Speed is defined as the distance travelled by an object per unit time.

Teacher's Note:
a) Speed is a scalar quantity, whereas velocity is the rate of change of displacement (a vector quantity).
b) The SI unit of both speed and velocity is metre per second (\( \text{m/s} \)).

9. Sound is produced by __________ objects. [1 Mark]
(a) vibrating
(b) fast moving
(c) stationary
(d) rotating

Answer: (A) vibrating

Sound is a form of energy produced by to-and-fro or back-and-forth motion known as vibration.

Teacher's Note:
a) Vibration is the rapid reciprocating motion of particles of an elastic medium.
b) Without a vibrating body, sound waves cannot be generated.

10. Air is a ___________ conductor of electricity while water is a __________ conductor of electricity [1 Mark]
(a) good, bad
(b) bad, good
(c) good, very good
(d) bad, very bad

Answer: (B) bad, good (the marking scheme also accepts option (d))

Dry air is a poor conductor (bad conductor) of electricity, while tap water containing dissolved salts conducts electricity.

Teacher's Note:
a) Pure distilled water is a bad conductor of electricity, but normal water containing minerals is a fair conductor.
b) Air acts as an insulator under normal conditions, breaking down only under very high voltages to cause sparks.

11. In which of the following, is the transfer of heat by convection currents impossible. [1 Mark]
(a) Oil
(b) Milk
(c) Water
(d) Metal

Answer: (D) Metal

Heat transfer by convection currents requires actual movement of particles, which is impossible in solids like metals where conduction takes place.

Teacher's Note:
a) Convection takes place only in fluids (liquids and gases).
b) In solids, heat is transferred primarily through conduction.

12. What kind of image is formed by a plane mirror? [1 Mark]
(a) Real and inverted
(b) Real and erect
(c) Virtual and erect
(d) Virtual and inverted

Answer: (C) Virtual and erect

A plane mirror always forms a virtual, erect, and laterally inverted image of the same size as the object.

Teacher's Note:
a) Virtual images cannot be caught on a screen because light rays do not actually intersect at the image position.
b) Lateral inversion means the left side of the object appears as the right side in the image.

13. Why does ice float on water? [1 Mark]
(a) Because density of ice is higher than that of water.
(b) Because density of ice is less than that of water.
(c) Because density of ice and water is the same but ice is a solid.
(d) Ice does not float on water.

Answer: (B) Because density of ice is less than that of water.

Any substance with a density lower than that of liquid water will float on it; ice has a lower density due to its cage-like crystalline structure.

Teacher's Note:
a) Water expands upon freezing, causing its volume to increase and its density to decrease.
b) The density of ice is approximately \( 0.917\text{ g/cm}^3 \), which is less than \( 1\text{ g/cm}^3 \) for water.

14. When is a body said to be in motion? [1 Mark]
(a) When it moves in a straight line
(b) When it moves in a circular path
(c) When it move in a swinging motion
(d) All of the above

Answer: (D) All of the above

A body is in motion if it changes its position with respect to its surroundings over time, regardless of the path shape.

Teacher's Note:
a) Motion is relative and can take various forms such as rectilinear, circular, or oscillatory.
b) Any change in position constitutes motion.

15. A switch is said to be OFF if it ________ the path of current flow. [1 Mark]
(a) makes
(b) breaks
(c) completes
(d) none of the above

Answer: (B) breaks

An OFF switch creates a gap in the circuit, thus breaking the path and stopping electric current flow.

Teacher's Note:
a) A closed (ON) switch completes the circuit.
b) An open (OFF) switch introduces a break in the conducting loop.

Question 2

(A) Answer the following questions in one word or one sentence. [5]

1. Name the unit in which frequency of an oscillating body is measured. [1 Mark]

Answer: Hertz (\( \text{Hz} \)).

Teacher's Note:
a) One hertz is equal to one oscillation per second.
b) Named after the physicist Heinrich Hertz.

2. Give the relation between acceleration, change in velocity and time. [1 Mark]

Answer: Acceleration = (Change in velocity) / (Time taken), or \( a = \frac{v - u}{t} \).

Teacher's Note:
a) Here \( u \) is initial velocity, \( v \) is final velocity, and \( t \) is time.
b) SI unit of acceleration is \( \text{m/s}^2 \).

3. Name the cell which can be recharged. [1 Mark]

Answer: Secondary cell.

Teacher's Note:
a) Secondary cells (such as lead-acid accumulators) can be recharged by passing an electric current through them in the opposite direction.
b) Primary cells cannot be recharged.

4. What are the ways by which heat transfer occurs from one place to other? [1 Mark]

Answer: Conduction, convection, and radiation.

Teacher's Note:
a) Conduction occurs mainly in solids, convection in fluids, and radiation does not require a material medium.
b) All three are fundamental modes of thermal energy transfer.

5. Name two types of spherical mirrors. [1 Mark]

Answer: Concave mirror and convex mirror.

Teacher's Note:
a) A concave mirror is curving inward, while a convex mirror bulges outward.
b) Both are segments of a hollow sphere.

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

1. S.I. unit of weight is ___________. [1 Mark]

Answer: S.I. unit of weight is Newton.

Teacher's Note:
a) Weight is a force, so its SI unit is Newton (\( \text{N} \)).
b) Mass is measured in kilograms (\( \text{kg} \)).

2. Metals are ___________ conductors of electricity. [1 Mark]

Answer: Metals are good conductors of electricity.

Teacher's Note:
a) Free electrons present in metals allow electric current to pass through them easily.
b) Silver and copper are among the best metallic conductors.

3. The straight line passing through the centre of curvature and pole of a spherical mirror is called its ___________. [1 Mark]

Answer: The straight line passing through the centre of curvature and pole of a spherical mirror is called its principal axis.

Teacher's Note:
a) The principal axis is normal to the mirror surface at the pole.
b) All principal rays and focal lengths are measured along or parallel to this axis.

4. Pitch of the sound depends on ___________. [1 Mark]

Answer: Pitch of the sound depends on frequency.

Teacher's Note:
a) Higher frequency corresponds to higher pitch (shrill sound).
b) Lower frequency corresponds to lower pitch (grave sound).

5. A stone tied to a string has ___________ motion when it is whirled around. [1 Mark]

Answer: A stone tied to a string has circular motion when it is whirled around.

Teacher's Note:
a) Circular motion involves movement along a circular path at constant or varying speed.
b) The tension in the string provides the necessary centripetal force.

Question 3

(A) Match the items in column A with the appropriate items in column B. [5]

Answer:
1. Sonar - Echo
2. Wood - Opaque
3. Graphite - Conductor
4. Ampere - Current
5. \( \text{kg/m}^3 \) - Density

Teacher's Note:
a) Matching questions test cross-topic associations and definitions.
b) Ensure proper pairing according to standard physics terminology.

(B) Define the following: [5]

1. Rest [1 Mark]

Answer: When the position of a body with respect to its surroundings does not change with time, the body is said to be at rest.

Teacher's Note:
a) Rest and motion are relative terms depending on the observer's frame of reference.
b) An object at rest has zero velocity relative to its reference point.

2. Convection [1 Mark]

Answer: The process of heat transfer when molecules actually come to the source of heat and then after absorbing heat energy move away from it.

Teacher's Note:
a) Convection involves the actual bulk movement of fluid particles.
b) It is responsible for sea breezes, land breezes, and ocean currents.

3. Timbre or quality [1 Mark]

Answer: Timbre or sound quality is that characteristic by virtue of which we can distinguish between sounds of the same pitch and loudness produced by two different musical instruments or by different voices.

Teacher's Note:
a) Quality depends on the waveform and the presence of overtones.
b) It helps us identify who is speaking even without seeing them.

4. Reflected ray [1 Mark]

Answer: The ray of light which bounces back from the surface of an object is called a reflected ray of light.

Teacher's Note:
a) The angle of reflection equals the angle of incidence.
b) It travels in the same medium from which the incident ray came.

5. Mass [1 Mark]

Answer: Mass is the amount of matter present in a body.

Teacher's Note:
a) Mass is a scalar quantity and remains constant everywhere.
b) Its SI unit is the kilogram (\( \text{kg} \)).

Question 4

(A) Identify and classify the following types of motions as rotatory, vibratory, oscillatory, rectilinear, curvilinear, or random motion: [5]

Answer:
As set in the table above, each motion is correctly classified based on its trajectory and characteristics.

Teacher's Note:
a) Rectilinear motion is motion along a straight line.
b) Rotatory motion involves rotation about a fixed axis.

(B) Give one word for the following [5]

1. The emission of light from living organisms like plants and animals. [1 Mark]

Answer: Bioluminescence.

Teacher's Note:
a) Fireflies and certain marine organisms exhibit bioluminescence.
b) It is produced by biochemical reactions inside the organism.

2. The force with which the Earth attracts a body towards its centre. [1 Mark]

Answer: Weight.

Teacher's Note:
a) Weight varies depending on the acceleration due to gravity (\( g \)).
b) Calculated as \( W = m \times g \).

3. A device used to either break the electric circuit or to complete it. [1 Mark]

Answer: Switch.

Teacher's Note:
a) A switch acts as a control valve for electric current.
b) It can be manual or automated.

4. The time taken by a freely oscillating pendulum to complete one oscillation. [1 Mark]

Answer: Time period.

Teacher's Note:
a) Denoted by symbol \( T \).
b) Measured in seconds.

5. The shadow cast by heavenly bodies on each other. [1 Mark]

Answer: Eclipse.

Teacher's Note:
a) Solar and lunar eclipses are classic examples.
b) Caused by the rectilinear propagation of light forming umbra and penumbra regions.

Question 5

(A) State whether the following statements are True or False [5]

1. Fuses should be connected to the neutral wire [1 Mark]

Answer: False. (Correct statement: Fuses should be connected to the live wire.)

Teacher's Note:
a) Connecting a fuse to the live wire ensures the current is cut off before reaching appliances during a fault.
b) Connecting it to the neutral wire would leave the appliance live even if the fuse blows.

2. The S.I. unit of relative density is \( \text{kg/m}^3 \). [1 Mark]

Answer: False. (Correct statement: Relative density has no unit.)

Teacher's Note:
a) Relative density is the ratio of two similar quantities (density of substance to density of water).
b) Being a ratio, it is a dimensionless quantity.

3. Heat always flows from a hotter object to a colder object. [1 Mark]

Answer: True.

Teacher's Note:
a) This is the fundamental second law of thermodynamics principle regarding heat flow direction.
b) Heat transfer stops when thermal equilibrium is reached.

4. Sound propagates faster through solids than through liquids. [1 Mark]

Answer: True.

Teacher's Note:
a) Sound travels fastest in solids due to high elasticity and closely packed molecules.
b) Speed in steel is much higher than in water or air.

5. A pinhole camera forms only black and white images. [1 Mark]

Answer: False. (Correct statement: The image in a pinhole camera is of the same colour as the object.)

Teacher's Note:
a) Pinhole cameras capture real, inverted images reflecting the actual colours of objects.
b) Colour information is preserved because light rays travel straight through the pinhole.

(B)

1. State three ways of conserving electric energy at home. [2 Marks]

Answer:
1. Put off all the fans and lights in a room when you leave that room.
2. Use tube lights or LED bulbs instead of traditional incandescent bulbs.
3. Switch off electrical appliances like televisions and air conditioners when not in use.

Teacher's Note:
a) Energy conservation helps reduce electricity bills and environmental pollution.
b) Switching off standby power devices saves significant energy over time.

2. What are transparent objects, translucent objects and opaque objects? Give examples. [3 Marks]

Answer:
1. Transparent objects: Objects that allow light to pass through them completely, allowing clear vision through them. Example: A clear empty glass, a window pane.
2. Translucent objects: Objects that allow only some light to pass through them while scattering the rest. Example: Thin tissue paper, frosted glass, tinted car windows.
3. Opaque objects: Objects that do not allow any light to pass through them; light is either absorbed or reflected. Example: Cardboard, bricks, wood.

Teacher's Note:
a) Classification depends on how light interacts with the material's atomic structure.
b) Opaque objects cast distinct shadows when placed in the path of light.

Question 6
Answer the following questions in short:

1. What do you mean by sublimation? Give examples of substances that sublime. [2 Marks]

Answer:
The process in which a solid directly goes into its gaseous state without passing through the intermediate liquid state is called sublimation.
Examples: Naphthalene, ammonium chloride, camphor.

Teacher's Note:
a) The reverse process of gas turning directly into solid is called deposition.
b) Sublimation occurs when vapor pressure equals external pressure at temperatures below the melting point.

2. A cork floats in water, while an iron nail sinks. Give reason. [2 Marks]

Answer:
A cork floats in water because its density is less than that of water, making the upward thrust (buoyant force) greater than its weight. On the other hand, an iron nail sinks because its density is greater than water, and the upthrust of water on the nail is less than its weight.

Teacher's Note:
a) Floating and sinking depend on the relative densities of the object and the fluid.
b) Archimedes' principle governs the magnitude of the upthrust experienced by immersed bodies.

3. If an object is placed at a distance of 10 cm in front of a plane mirror, how far would the object be from its image? [2 Marks]

Answer:
The object would be 20 cm away from its image.
Working:
Distance of object from mirror = 10 cm.
Distance of image from mirror = 10 cm.
Total distance between object and image = 10 cm + 10 cm = 20 cm.

Teacher's Note:
a) In a plane mirror, object distance equals image distance.
b) Students must remember to sum both distances when asked for the separation between object and image.

4. Why are copper and aluminium used for making wires? [2 Marks]

Answer:
Copper and aluminium are used for making wires because they are very good conductors of electricity with low electrical resistance, allowing electric current to pass through them efficiently with minimal energy loss.

Teacher's Note:
a) Both metals are also ductile, meaning they can be easily drawn into thin wires.
b) Copper has exceptionally high conductivity, while aluminium is lighter and more economical for long-distance transmission.

5. What are the three main properties of sound waves? [2 Marks]

Answer:
1. Loudness: The measure of heaviness or volume of a sound, depending on its amplitude.
2. Pitch: The measure of shrillness of a sound, depending on its frequency.
3. Quality (Timbre): The characteristic that enables us to distinguish between different sounds of the same pitch and loudness.

Teacher's Note:
a) These are the three subjective characteristics of musical sound.
b) Amplitude affects loudness, frequency affects pitch, and waveform affects quality.

Question 7

(A)

1. How is the density of an irregularly shaped solid such as a stone determined? [4 Marks]

Answer:
The density of an irregularly shaped solid (insoluble in water) such as a stone is determined as follows:
1. Find the mass of the stone using a beam balance and let it be \( M \).
2. Take a measuring cylinder partially filled with water and note the initial water level reading \( V_1 \).
3. Immerse the stone completely into the water inside the cylinder and note the new water level reading \( V_2 \).
4. Calculate the volume of the stone as \( V = V_2 - V_1 \).
5. Calculate the density using the formula: Density = Mass / Volume = \( \frac{M}{V_2 - V_1} \).

Teacher's Note:
a) This method is known as water displacement method.
b) The solid must be insoluble in water and denser than water so it sinks completely.

2. A body moving with a velocity 5 m/s achieves a velocity of 20 m/s in 30 s. Calculate the acceleration of the body? [3 Marks]

Answer:
Given data:
Initial velocity (\( u \)) = 5 m/s
Final velocity (\( v \)) = 20 m/s
Time taken (\( t \)) = 30 s
Formula: \( a = \frac{v - u}{t} \)
Substitution: \( a = \frac{20\text{ m/s} - 5\text{ m/s}}{30\text{ s}} \)
Calculation: \( a = \frac{15\text{ m/s}}{30\text{ s}} = 0.5\text{ m/s}^2 \)
Final Answer: Acceleration = \( 0.5\text{ m/s}^2 \).

Teacher's Note:
a) Always write formula, substitution, and final answer with correct SI units to secure full marks.
b) Check that subtraction in the numerator is performed correctly before dividing by time.

(B)

1. State the characteristics of an image formed by a concave mirror when the object is placed at the focus. Explain with a ray diagram [3 Marks]

Answer:
Characteristics of the image formed by a concave mirror when the object is placed at the focus (\( F \)):
1. Image formed is real.
2. Image formed is inverted.
3. It is highly magnified.
4. Image is formed at infinity.

[Figure: Ray diagram showing a concave mirror with pole P, focus F, and centre of curvature C. An object AB is placed upright at F. A ray parallel to the principal axis passes through F after reflection. A ray passing through F goes parallel to the principal axis after reflection. The reflected rays are parallel and meet at infinity, forming a highly magnified real and inverted image.]

Teacher's Note:
a) When an object is at the focus of a concave mirror, reflected rays become parallel and never intersect on the finite page, forming the image at infinity.
b) Ensure arrows are marked properly on incident and reflected rays in the ray diagram.