NSAA 2020 Physics PART B

The diagram represents the structure of a charged atom (ion) of one isotope of an element.

Which diagram represents the structure of an oppositely charged ion of a different isotope of the same element?

• A.Diagram A
• B.Diagram B
• C.Diagram C
• D.Diagram D
• E.Diagram E
• F.Diagram F
• G.Diagram G

Answer: B

• A.160 J
• B.500 J
• C.1340 J
• D.1500 J
• E.1660 J
• F.1840 J
• G.2500 J

Answer: C

A water wave is travelling in a shallow tank of water. The wave passes from region X into region Y where the speed of the wave differs from that in region X. The diagram shows the directions of travel in the two regions and peaks of the wave that are separated by one wavelength.

In region X, the angle between the wave peaks and the boundary between the regions is $\theta$.

In region Y, the angle between the wave peaks and the boundary is $\phi$.

What are the angle of incidence and the angle of refraction, and in which region is the speed of the wave greater?

• A.angle of incidence: $\theta$, angle of refraction: $\phi$, speed greater in region: X
• B.angle of incidence: $\theta$, angle of refraction: $\phi$, speed greater in region: Y
• C.angle of incidence: $\theta$, angle of refraction: $90° - \phi$, speed greater in region: X
• D.angle of incidence: $\theta$, angle of refraction: $90° - \phi$, speed greater in region: Y
• E.angle of incidence: $90° - \theta$, angle of refraction: $\phi$, speed greater in region: X
• F.angle of incidence: $90° - \theta$, angle of refraction: $\phi$, speed greater in region: Y
• G.angle of incidence: $90° - \theta$, angle of refraction: $90° - \phi$, speed greater in region: X
• H.angle of incidence: $90° - \theta$, angle of refraction: $90° - \phi$, speed greater in region: Y

Answer: D

A sample of an ideal gas is sealed in a cylindrical container by a piston as shown in the diagram.

The particles of the gas are moving with an average speed v, and collide with the surface of the piston with a frequency f.

The piston is now slowly pushed into the cylinder until the gas occupies half of its original volume, but the gas remains at the same temperature.

What is the new average speed of the particles of the gas, and at what frequency do they now collide with the surface of the piston?

• A.average speed: $2v$, frequency: $\frac{1}{2}f$
• B.average speed: $2v$, frequency: $f$
• C.average speed: $2v$, frequency: $2f$
• D.average speed: $v$, frequency: $\frac{1}{2}f$
• E.average speed: $v$, frequency: $f$
• F.average speed: $v$, frequency: $2f$

Answer: D

In a laboratory, liquid nitrogen is stored at a very low temperature in the vessel shown in the diagram.

The vessel has a double wall made from a poor thermal conductor. There is a vacuum in the gap between the two walls.

The inner surface of the inner wall is shiny. The outer surface of the outer wall is shiny.

These features insulate the liquid nitrogen by reducing the rate at which thermal energy is transferred to the liquid nitrogen.

Which of the following statements explain(s) why these features help to insulate the liquid nitrogen?

1 The shiny inner surface of the inner wall is a good emitter of thermal radiation.
2 Thermal radiation cannot travel in a vacuum.
3 The shiny outer surface of the outer wall is a poor absorber of radiation.

• A.none of them
• B.1 only
• C.2 only
• D.3 only
• E.1 and 2 only
• F.1 and 3 only
• G.2 and 3 only
• H.1, 2 and 3

Answer: G

• A.6
• B.8
• C.10
• D.12
• E.14
• F.16

Answer: A

• A.efficiency %: 20, energy wasted every minute / J: $9.6 \times 10^9$
• B.efficiency %: 20, energy wasted every minute / J: $3.84 \times 10^{10}$
• C.efficiency %: 20, energy wasted every minute / J: $4.8 \times 10^{10}$
• D.efficiency %: 80, energy wasted every minute / J: $9.6 \times 10^9$
• E.efficiency %: 80, energy wasted every minute / J: $3.84 \times 10^{10}$
• F.efficiency %: 80, energy wasted every minute / J: $4.8 \times 10^{10}$

Answer: F

The primary coil of an ideal, 100% efficient transformer is connected to a 240 V mains supply.

A lamp L that is connected to the secondary coil has a voltage of 12V across it. An identical lamp and a switch S are also connected to the transformer as shown in the diagram.

With the switch open, the current in the primary coil is 0.10A.

The switch is now closed.

What is the current in the primary coil now and what is the current in lamp L?

• A.current in primary coil / A: 0.10, current in lamp L / A: 1.0
• B.current in primary coil / A: 0.10, current in lamp L / A: 2.0
• C.current in primary coil / A: 0.10, current in lamp L / A: 4.0
• D.current in primary coil / A: 0.20, current in lamp L / A: 1.0
• E.current in primary coil / A: 0.20, current in lamp L / A: 2.0
• F.current in primary coil / A: 0.20, current in lamp L / A: 4.0

Answer: C

Two fixed horizontal metal rails are side by side and 12cm apart. The rails are connected to a dc power supply by a switch that is initially open.

A freely moveable metal rod of length 20 cm is placed on the rails as shown in the diagram. The diagram shows the arrangement seen from above.

The angle between the rod and the rails is 90°.

The whole arrangement is placed in a uniform magnetic field of magnitude 0.50 T that is directed perpendicularly into the page.

The moveable rod has a weight of 0.40 N.

The switch is now closed. As a result, there is a current of 2.4 A in the circuit and the rod moves.

What is the initial magnitude of the acceleration of the rod and what is its direction?

(gravitational field strength = 10 N kg⁻¹)

• A.acceleration / ms⁻²: 0.36, direction: to the left
• B.acceleration / ms⁻²: 0.36, direction: to the right
• C.acceleration / ms⁻²: 0.60, direction: to the left
• D.acceleration / ms⁻²: 0.60, direction: to the right
• E.acceleration / ms⁻²: 3.6, direction: to the left
• F.acceleration / ms⁻²: 3.6, direction: to the right
• G.acceleration / ms⁻²: 6.0, direction: to the left
• H.acceleration / ms⁻²: 6.0, direction: to the right

Answer: B

A circuit contains a 12V battery, a thermistor and a fixed resistor connected in series. The graph shows how the resistance of the thermistor varies with temperature.

When the temperature of the thermistor is 10°C the current in the circuit is 25 mA.

What is the current when the temperature of the thermistor is 80 °C?

• A.30 mA
• B.80 mA
• C.100 mA
• D.120 mA
• E.150 mA
• F.300 mA
• G.480 mA

Answer: C

• A.2.0J
• B.18 J
• C.20 J
• D.28 J
• E.35 J
• F.40 J
• G.45 J
• H.65 J

Answer: B

• A.Infrared waves are emitted, but not ultraviolet or visible light waves.
• B.Infrared and visible light waves are emitted, but not ultraviolet waves.
• C.Infrared, ultraviolet and visible light waves are all emitted.
• D.Ultraviolet waves are emitted, but not infrared or visible light waves.
• E.Ultraviolet and visible light waves are emitted, but not infrared waves.

Answer: E

• A.2880 g
• B.3240 g
• C.3600 g
• D.3840 g
• E.4320 g
• F.4800 g

Answer: E

A car of mass 800 kg travels in a straight line along a horizontal road.

The car accelerates non-uniformly from rest for 5.0 seconds and then moves at constant speed, as shown in the distance-time graph:

What is the average resultant force acting on the car over the time for which it is accelerating?

• A.320 N
• B.480 N
• C.640 N
• D.960 N
• E.1600 N
• F.3200 N
• G.4800 N

Answer: D

• A.background count rate / cpm: 224, third measurement / cpm: 148
• B.background count rate / cpm: 224, third measurement / cpm: 226
• C.background count rate / cpm: 142, third measurement / cpm: 28
• D.background count rate / cpm: 142, third measurement / cpm: 148
• E.background count rate / cpm: 142, third measurement / cpm: 154
• F.background count rate / cpm: 14, third measurement / cpm: 14
• G.background count rate / cpm: 14, third measurement / cpm: 28
• H.background count rate / cpm: 14, third measurement / cpm: 42

Answer: G

• A.2.1 ms⁻¹
• B.3.4 ms⁻¹
• C.5.0ms⁻¹
• D.7.5 ms⁻¹
• E.20 ms⁻¹

Answer: C

• A.1 535 000 J
• B.1 624 000 J
• C.1 649 000 J
• D.1 663 000 J
• E.1 726 000 J

Answer: D

• A.$\frac{\rho_L g}{Vrk}$
• B.$\frac{\rho_s g}{Vrk}$
• C.$\frac{g(\rho_s - \rho_L)}{Vrk}$
• D.$\frac{g(\rho_s + \rho_L)}{Vrk}$
• E.$\frac{V\rho_L g}{rk}$
• F.$\frac{V\rho_s g}{rk}$
• G.$\frac{Vg(\rho_s - \rho_L)}{rk}$
• H.$\frac{Vg(\rho_s + \rho_L)}{rk}$

Answer: G

• A.It is increasing at an increasing rate.
• B.It is increasing at a constant rate.
• C.It is increasing at a decreasing rate.
• D.It is not changing.
• E.It is decreasing at an increasing rate.
• F.It is decreasing at a constant rate.
• G.It is decreasing at a decreasing rate.

Answer: A

• A.0 ms⁻¹
• B.4.0 ms⁻¹
• C.6.0 ms⁻¹
• D.12 ms⁻¹
• E.16 ms⁻¹
• F.$\sqrt{6}$ ms⁻¹
• G.$\sqrt{12}$ ms⁻¹
• H.$\sqrt{30}$ ms⁻¹

Answer: G