11 mark
The r.m.s. voltage of the output from a low-voltage a.c. supply is 18·0 V. The peak voltage of the output is
Electricity · Practice Test A
Higher Physics · Electricity
Practice Test A
Answer everything, then mark it in one go.
45marks
60 minsuggested
14questions
Have your jotter and a pen beside you. Do every calculation in your jotter, showing the relationship, the substitution and the final answer with its unit, exactly as you would in the exam — this page asks you only for the relationship you used and your final answer.
Powers of ten can be typed any way you like — 2.5e4, 2.5*10^4, 2.5x10^4 or 2·5 × 10⁴ are all read the same.
Nothing is timed and nothing is sent anywhere — your answers stay on this device, so you can close the tab and come back.
Relationships you may need
| Quantity | Relationship |
|---|---|
| Peak and r.m.s. | Vpeak = √2 Vrms Ipeak = √2 Irms |
| Period and frequency | T = 1 / f |
| Charge and current | Q = It |
| Resistance and power | V = IR P = IV = I2R = V2 / R |
| Combining resistors | RT = R1 + R2 + … 1 / RT = 1 / R1 + 1 / R2 + … |
| E.m.f. and internal resistance | E = V + Ir |
| Potential divider | V1 = (R1 / (R1 + R2)) VS |
| Capacitance and energy stored | C = Q / V E = ½QV = ½CV2 = ½Q2 / C |
Working goes in your jotter. On this page you give the relationship and the final answer only — the mark scheme at the end shows the substitution you should have written down.
Warm-up
8 marksEveryone should aim for full marks here. One step, no rearranging.
21 mark
The output from a signal generator is displayed on an oscilloscope. The trace is shown. The timebase of the oscilloscope is set at 2·5 ms/div. The frequency of the output signal is
31 mark
The power dissipated in a 220 Ω resistor is 0·55 W. The current in the resistor is
41 mark
A circuit is set up as shown. The battery has negligible internal resistance. The reading on the voltmeter is
51 mark
A battery of e.m.f. 6·5 V and internal resistance 0·60 Ω is connected to a resistor of resistance 4·4 Ω as shown. The lost volts due to the internal resistance of the battery is
61 mark
A 43 μF capacitor is charged until the potential difference across it is 45 V. The charge stored on the capacitor is
71 mark
An uncharged capacitor is connected in series with a resistor, a switch and a d.c. supply of negligible internal resistance. The switch is closed and the capacitor charges. A student makes the following statements.
- The charging current is greatest at the instant the switch is closed.
- Using a resistor of greater resistance increases the maximum charge stored on the capacitor.
- Using a supply of greater voltage increases the maximum energy stored in the capacitor.
81 mark
Which of the following describes the conduction band, and the gap between the valence band and the conduction band, in a pure semiconductor at room temperature?
Core
24 marksThe demand of the real test — one rearrangement, one conversion or one intermediate step.
97 marks
The output of a signal generator is connected across a 33 Ω resistor. An oscilloscope connected across the resistor shows the trace below. The Y-gain setting is 2·0 V/div and the timebase setting is 0·5 ms/div.
(a) Determine the peak voltage of the signal.1
(b) Determine the frequency of the signal.2
(c) Calculate the r.m.s. voltage of the signal.2
(d) Calculate the r.m.s. current in the resistor.2
106 marks
A student uses the circuit shown to determine the e.m.f. E and internal resistance r of a battery. The variable resistor provides known values of resistance R. For each value of R the switch is closed, the current I is noted and 1/I is calculated.
Applying conservation of energy to the circuit gives R = E × (1/I) − r, which is the equation of a straight line: the gradient is E and the intercept on the R axis is −r. The graph of the student's results is shown.
(a) Use the graph to determine the internal resistance of the battery.1
(b) Use the graph to determine the e.m.f. of the battery.2
(c) The battery is accidentally short-circuited. Calculate the current in the battery when this happens.3
117 marks
A 330 μF capacitor is charged using the circuit shown. The 5·0 V battery has negligible internal resistance. The capacitor is initially uncharged. The switch S is closed, and the charging current is kept constant at 25 μA by adjusting the resistance of the variable resistor R.
(a) Calculate the resistance of the variable resistor R just after the switch is closed.3
(b) Calculate the charge on the capacitor 36 s after the switch is closed.2
(c) Explain why the resistance of the variable resistor must be decreased as the capacitor charges, to keep the current constant.2
124 marks
An intruder alarm uses a beam of light shining onto a photodiode. A photodiode is a p–n junction. While light is incident on the photodiode it produces a potential difference; when an intruder breaks the beam, the potential difference drops and the alarm sounds.
(a) Using band theory, explain how a potential difference is produced when photons of light are incident on the photodiode.3
(b) Explain, in terms of the conduction band, why the potential difference drops when the beam is broken.1
Push
13 marksTwo or more steps, an unfamiliar context, and a judgement to justify.
138 marks
A battery of e.m.f. 6·8 V and internal resistance 2·4 Ω is connected to a variable resistor R as shown. The resistance of R is set to 1·6 Ω.
(a) Calculate the current in the circuit.3
(b) Calculate the power dissipated in the variable resistor.3
(c) The resistance of R is now increased to 2·4 Ω. State whether the power dissipated in R increases, decreases or stays the same. You must justify your answer by calculation.2
145 marks
An emergency exit sign contains a 120 mF capacitor. While mains power is on, the capacitor is kept charged to 3·3 V. During a power cut the capacitor discharges through a small lamp, keeping the sign lit for a short time.
(a) Calculate the maximum energy stored in the capacitor.3
(b) The capacitor is replaced by one of greater capacitance, which is also kept charged to 3·3 V. State the effect this has on the time the lamp stays lit during a power cut. You must justify your answer.2
Your result
0out of 45
0%percentage
—indicative band
Bands are indicative only — they are a guide to where you are, not a grade.
Sources & credits: questions are adapted from Higher Physics past papers, reproduced and adapted for educational use — past papers and marking instructions © Qualifications Scotland (SQA). Numbers, circuits and contexts have been changed, and some questions are original to this site. Circuit diagrams, oscilloscope traces, graphs and band diagrams drawn for this site © R Stewart Physics, Electronics and Engineering, 2026.