Cambridge IGCSE Physics - 0625 - Core Paper 3 2021 Summer Zone 2

Fig. 1.1 shows the core of a transformer. It is made from thin sheets of iron.
(a) There are 200 sheets of iron in the core of the transformer. The thickness of the core is 50 mm. Calculate the average thickness of one sheet of iron.
average thickness of one sheet = ................................................ mm [3]
(b) The density of the iron in the core is 7.65 g/cm³. The mass of the core is 1377 g. Calculate the volume of the core.
volume = ................................................ cm³ [3]
(c) State the name of a device used to measure mass. .............................................................................................................................. [1]

Fig. 2.1 shows how the speed of a car varies between 0 and 60.0 s.

(a) Determine the speed of the car using information from Fig. 2.1:
(i) when the time is 5.0 s
speed = .................................................. m/s [2]
(ii) when the car is moving with a constant speed.
speed = .................................................. m/s [1]
(b) Describe how the speed of the car changes between 30.0 s and 60.0 s.
....................................................................................................................... [2]
(c) Determine the distance travelled by the car between 10.0 s and 30.0 s.
distance travelled = .................................................. m [3]
(d) The total distance travelled by the car in the last 30.0 s is 226 m.
Calculate the average speed of the car in the last 30.0 s.
average speed = .................................................. m/s [3]
[Total: 11]

Fig. 3.1 shows a barrier used at a car park. The beam can be raised and lowered by a man rotating it about its pivot.



(a) The weight of the beam is 150 N. This acts at a distance of 1.8 m from the pivot as shown in Fig. 3.1.
Calculate the moment of the weight of the beam about the pivot.
Include the correct unit in your answer.

moment of weight of beam = ................................. unit ............... [4]

(b) When the weight $W$ of the heavy weight acts at a distance of 0.6 m from the pivot, the barrier is horizontal and balanced as shown in Fig. 3.1.
The man raises the barrier and the heavy weight slips to a distance of 0.8 m from the pivot.
This causes a problem for the man trying to lower the barrier.

Describe and explain the problem this causes for the man lowering the barrier.
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................................................................................................................................................................................... [3]

A student investigates energy changes when a ball rolls down a curved track.
The student holds the ball at a starting point on the curved track, as shown in Fig. 4.1.

The ball is released. It rolls down the track, up the other side to the stopping point and then back down again.
(a) Describe the energy changes that take place as the ball rolls from the starting point to the stopping point.
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....................................................................................................................................................... [4]
(b) The height of the stopping point is less than the height of the starting point.

Describe how the principle of conservation of energy explains the difference between the height of the stopping point and the height of the starting point.
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....................................................................................................................................................... [2]
[Total: 6]

Fig. 5.1 shows a device connected to a gas cylinder. The device is used to measure the pressure of the gas inside the cylinder.

(a) (i) State the name of the device shown in Fig. 5.1.
........................................................ [1]

(ii) The atmospheric pressure is equal to 75 cm of mercury.
Determine the pressure of the gas in the cylinder. Use information from Fig. 5.1.
pressure of gas = ............................ cm of mercury [2]

Fig. 5.2 shows two identical heavy stone tiles placed on soft ground. One is vertical and the other is horizontal.

One of the tiles sinks into the soft ground.
State and explain which tile sinks into the soft ground.
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........................................................................................ [4]

(a) Fig. 6.1 shows a liquid-in-glass thermometer. [Image_1: Fig. 6.1]
The thermometer has a bulb made from thin glass and a narrow tube.
(i) State the temperature indicated on the thermometer in Fig. 6.1.
....................................................... [1]
(ii) Explain why:
1. the bulb is made from thin glass
....................................................... [1]
2. the tube, along which the liquid expands, is narrow.
....................................................... [1]
(b) A substance cools from $40\,^{\circ}\text{C}$ to $-20\,^{\circ}\text{C}$.
The substance takes $40$ minutes to cool from $40\,^{\circ}\text{C}$ to its melting point of $-12\,^{\circ}\text{C}$.
The substance then takes $20$ minutes to freeze.
On Fig. 6.2, sketch a temperature–time graph as the substance cools from $40\,^{\circ}\text{C}$ to $-20\,^{\circ}\text{C}$.
[Image_2: Fig. 6.2]
[4]

(a) Both radio waves and $\gamma$-rays (gamma) are radiations in the electromagnetic spectrum. Fig. 7.1 shows the main regions of the electromagnetic spectrum. Most regions are labelled.

[Table_1]

(i) On Fig. 7.1, write the names of the radiations in the other two parts of the electromagnetic spectrum. [2]

(ii) State one use of $\gamma$-rays.
.............................................................................................................................. [1]

(iii) A star emits radio waves and $\gamma$-rays at the same time. They all travel across the vacuum of space to the Earth’s atmosphere.
State whether the radio waves or the $\gamma$-rays, if either, arrive first at the Earth’s atmosphere. Give a reason for your answer.
statement ....................................................... [2]
reason ...............................................................
............................................................................................................................ [2]

(b) Fig. 7.2 shows pulses of a signal from a star.



(i) Use the graph in Fig. 7.2 to determine the time between pulses.
time between pulses = .......................................................... s [2]

(ii) Determine the frequency of the pulses in Fig. 7.2.
frequency = .................................................... Hz [2]

[Total: 9]

A student uses a semicircular glass block to investigate refraction.

(a) He shines a ray of red light into the block, as shown in Fig. 8.1. X is the middle of the flat surface.



(i) On Fig. 8.1, draw the normal where the ray meets the flat surface at X. [1]
(ii) On Fig. 8.1, label the angle of refraction. Use the letter R for the label. [1]
(iii) The student uses a semicircular glass block. State the name of one other piece of equipment that he needs for the investigation. ................................................................................................................... [1]

(b) Fig. 8.2 shows a ray of red light incident on the flat surface of the semicircular glass block. The angle of incidence is greater than the critical angle for glass.



On Fig. 8.2, draw the path of the ray after it strikes the flat surface. [2]

(a) Fig. 9.1 shows an electric circuit.
[Image_1: Schematic diagram of an electric circuit with component X, light-dependent resistor (LDR), voltmeter (V), and ammeter (A)]

(i) The current in the metal wires of the circuit is a flow of particles. State the name of these particles.
................................................................................................................................................................................................................... [1]

(ii) State the name of component X.
................................................................................................................................................................................................................... [1]

(iii) The circuit is in a darkened room. The voltmeter reading is 5.5 V and the ammeter reading is 0.050 A.

Calculate the resistance of the light-dependent resistor (LDR).

resistance = ........................................................... Ω [3]

(b) The light in the room is switched on. The room becomes bright.

State and explain how increasing the brightness of the light that falls on the LDR changes the current in the circuit.
...................................................................................................................................................................................................................
................................................................................................................................................................................................................... [2]

Fig. 10.1 shows an electric screwdriver which has an electric motor and a battery. (a) (i) The electric motor has a current-carrying coil in a magnetic field. The screwdriver’s manufacturer decides that the turning effect of the coil is too small. State three ways of increasing the turning effect of the coil.
1. .......................................................
2. .......................................................
3. ....................................................... [3]

(ii) The coil in the motor can rotate in either direction. State what happens in the coil to reverse the direction of rotation.
.................................................................................. [1]

(b) The battery is charged using a transformer connected to an a.c. power supply. The primary voltage $ V_p $ to the transformer is 234 V and the secondary voltage $ V_s $ of the transformer is 18 V. The number of turns on the primary coil $ N_p $ is 2470 turns. Calculate the number of turns on the secondary coil $ N_s $.
$ N_s $ = ............................................................... [3]

(a) The nuclide notation $^{A}_{Z}X$ describes the nucleus of an atom.
Draw a line from each symbol to the correct description of the symbol.

(b) The activity of a sample of a radioactive nuclide is measured in June of each year.
In June 2004 the activity was $80000$ counts/s.
In June 2014 the activity was $20000$ counts/s.
(i) Show that the half-life of the nuclide is $5$ years.
(ii) Determine the year when the activity of the sample was $10000$ counts/s.
year = ..........................................................