Form 4 Physics topical questions and answers on electronics

In this online learning session, we are going to solve form 4 physics questions on electronics. The questions are very useful to those preparing for KCSE exams as well as those revising class work.

Lessons (20)     SHARE

• 1.    Describe how a p-type semiconductor is formed
  2m 48s

• 2.    Using the components symbols shown in fig. 13, sketch a series circuit diagram for a forward biased diode.
  3m 30s

• 3.    (i) Distinguish between semiconductor and conductors. (ii) Give one example of a semiconductor and one for a conductor.
  1m 18s

• 4.    In the circuit in fig. 5, when the switch S is closed, the voltmeter shows a reading. When the cell terminals are reversed and the switch is closed, the voltmeter reading is zero. Explain these observations.
  4m 22s

• 5.    What is meant by donor impurity in semiconductors?
  1m 35s

• 6.    Explain how a p-type semiconductor is made from a pure semiconductor.
  3m 18s

• 7.    You are provided with 12V a.c source, four diodes and resistor. (i) Draw a circuit diagram for a full wave rectifier and show the points at which the output is taken. (ii) Sketch on axis provided, the graph of the output when a capacitor is put in parallel with the resistor in the circuit in (i) above.
  4m 39s

• 8.    Pure silicon can be changed into P-type semiconductor by adding an impurity. Explain how this is achieved.
  2m 18s

• 9.    Draw using appropriate symbols, the circuit diagram of a junction diode in reverse bias.
  2m 51s

• 10.    (a) Explain how doping producers an n-type semiconductor for a pure conductor material. (b) Figure 5 shows the circuit of a rectifier using four diodes #D_1, D_2, D_3 and D_4#. (i) Explain how a rectified output is produced from the set up when an a.c input is connected across AB. (ii) On the axis provided, sketch the graph of output voltage against time for rectifier. (iii) A capacitor is now
  5m 7s

• 11.    In the axes provided sketch the current- voltage characteristics for reverse-biased p-n junction.
  1m 18s

• 12.    You are provided with a diode, a resistor R, an a.c source of low voltage and connecting wires. In the space provided, sketch the circuit diagram for a half –wave rectifier and indicate the terminals where the output voltage V0 may be conncted.
  3m 54s

• 13.    Figure 6 (a) and (b) show a p-n junction connected to a battery. It is observed that the current in figure 6 (a) is greater than the current in figure 6 (b) State the reason for this.
  3m 30s

• 14.    Figure 7 shows a block diagram of a p-n junction diode. On the same diagram, show how a battery may be connected so that the diode is reverse biased.
  1m 42s

• 15.    (a) State what is meant by an extrinsic semiconductor (b) Figure 12 shows a depletion layer in an unbiased p-n junction State how a battery can be used to make the depletion layer narrower. (c) Figure 13 shows an incomplete circuit of a full wave rectifier. (i) Draw in the figure two more diodes to complete the circuit. (ii) Show on the figure the points across which the output of the rectifier
  6m 32s

• 16.    When a germanium crystal is doped with arsenic, it becomes an N-type semiconductor. Explain how the change occurs. (number of electrons in the outermost shell for germanium=4, arsenic =5)
  2m 53s

• 17.    Figure 5 shows a graph of current against voltage for a semiconductor diode . In the space provided, draw a circuit diagram that may be used to obtain values needed to draw the graph in figure 5.
  4m 58s

• 18.    Draw a circuit diagram to show a p-n junction diode in the forward biased mode.
  1m 56s

• 19.    (i) Draw a circuit showing the depletion layer of a p-n junction diode connected in the reverse bias mode. (ii) State the reason why increasing the external voltage in (i) makes the depletion layer wider. (iii) State the meaning of breakdown voltage of a junction diode (iv) State one application of diodes.
  4m 46s

• 20.    Figure 4 shows the input signals on a CRO screen when two diodes are used during a full wave rectification. Explain how the two diodes rectify the input signal.
  1m 53s

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