O-LevelPhysicsElectricity5054/22 · May/June 2020 · Q1015 Marks

An oscilloscope is a device used to display waveforms. (a) Inside the oscilloscope, a beam of electrons is emitted from a metal filament by thermionic emission. The emitted electrons are accelerated away from the filament by a potential difference of 2000 V.

(a)(i)State what must happen to the metal filament for thermionic emission to occur.[1]
(a)(ii)Explain why the electrons accelerate away from the filament.[1]
(a)(iii)The charge on one electron is 1.6 × 10-19С. Calculate the maximum kinetic energy of one electron after it has been accelerated through 2000V. kinetic energy =[2]
(b)(i)Fig. 10.1 is the trace on the screen of the oscilloscope. The settings on the oscilloscope are 10ms/division for the x-axis and 3.0V/division for the y-axis. [Figure 10.1] Calculate the amplitude of the trace shown in Fig. 10.1. amplitude =[2]
(b)(ii)Calculate the time for one oscillation (complete wavelength) of the trace shown in Fig. 10.1. time =[1]
(c)(i)The trace shown in Fig. 10.1 is caused by a sound. The sound travels through the air to a microphone from the place that it is made. The microphone is connected to the oscilloscope which displays the waveform shown. Sound is a type of wave. State which type.[1]
(c)(ii)Describe the motion of the air molecules as the sound passes through the air to the microphone.[2]
(c)(iii)Describe and explain how the trace on the screen changes as the pitch of the sound becomes higher. The settings on the oscilloscope are unchanged.[2]
(d)(i)A student investigates what happens when a diode is connected between the microphone and the oscilloscope. Fig. 10.2 shows the circuit that he uses. [Figure 10.2] Without the diode, the output from the microphone is an alternating current and the trace is as shown in Fig. 10.1 on page 18. Describe the action of the diode on the current from the microphone.[1]
(d)(ii)On the grid in Fig. 10.3, sketch the trace seen on the screen when the diode is used. [Figure 10.3][2]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (May/June 2020). The mark or mark type is shown in brackets.

[B1] filament is hot / heated
[B1] attracted by a positive potential or repelled by filament or filament is negative
[C1] 2000 × 1.6 × 10-19
[A1] 3.2 x 10-16 J
[C1] two divisions
[A1] 6(.0) V
[B1] 40 ms
[B1] longitudinal
[B1] oscillation described, e.g. back and forth
[B1] in direction of travel (of wave / energy) or compressions and rarefactions stated or described
[B1] more waves seen on screen
[B1] higher frequency (of sound) or more waves per second or time for one wave less
[B1] diode passes current in only one direction or current only flows for half the cycle / oscillation or current is d.c. / direct
[C1] at least one top half and no bottom half or one bottom half and no top half
[A1] three top halves of the wave and flat sections along mid line or two bottom halves of the wave and flat sections along mid line