These eight questions use original numbers. Write your own answer before you open the explanation.
This set goes with SPM Physics electronics. The timed original practice session builder turns it into a timed attempt.
Questions
Q1. A diode has its arrow pointing toward the negative terminal of a cell, in series with a lamp. Does the lamp light?
Answer
Yes. The current from the positive terminal enters at the arrow’s tail, so the diode is forward biased and conducts. The lamp lights.
Q2. A 9.0 V supply drives a forward-biased ideal diode in series with a 90 Ω resistor. Find the current.
Answer
I = V ÷ R = 9.0 ÷ 90 = 0.10 A, treating the diode as ideal.
Q3. Describe the output of a half-wave rectifier for a sinusoidal input.
Answer
The output is a row of humps, all in the same direction, one for each cycle. During the half cycle that reverse biases the diode the output is zero. The graph has a gap after each hump.
Q4. The mains is 50 Hz. How many output pulses each second does a full-wave bridge rectifier give?
Answer
Each half cycle gives one pulse, so 2 × 50 = 100 pulses each second.
Q5. What does a smoothing capacitor do in a rectifier?
Answer
It charges while the voltage rises and discharges through the load while the voltage falls. This fills the gaps between humps, so the output is nearer to a steady direct voltage, with a small ripple.
Q6. A 9 V supply has a 3 kΩ fixed resistor on top and a thermistor at the bottom, with the transistor base between them. The thermistor is 6 kΩ when cold. Find the base voltage, and state whether the transistor is on.
Answer
Base voltage = 9 × 6 ÷ (3 + 6) = 9 × 6 ÷ 9 = 6.0 V. This is above 0.7 V, so the transistor is on.
Q7. State what thermionic emission is and why a vacuum is used in the tube.
Answer
Thermionic emission is the release of electrons from a heated metal surface. A vacuum prevents the electrons colliding with air molecules, so the beam travels in a straight line to the screen.
Q8. An oscilloscope has Y-gain 1.0 V per division and time base 10 ms per division. The trace peaks 2.5 divisions above the centre, and one cycle spans 2 divisions. Find the peak voltage and the frequency.
Answer
Peak voltage = 2.5 × 1.0 = 2.5 V.
Period = 2 × 10 = 20 ms = 0.020 s, so frequency = 1 ÷ 0.020 = 50 Hz.
If you got these wrong
- Q1 and Q2: interpreting diode behaviour.
- Q3, Q4 and Q5: explaining rectification.
- Q6: reading transistor circuit functions.
- Q7 and Q8: electron beams and the oscilloscope.
Log slips in the mistake log. If you want a teacher to go through new circuits with you, see online one-to-one Physics tuition.