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(a) State the meaning of the following terms:
(i) Photoelectric effect.
(ii) Threshold frequency.
(b) Figure 5 shows some light incident on the cathode of a photocell.

The photocell is connected in series with a battery, variable resistor and micro ammeter.
(i) Explain how the micro ammeter reading is affected when the intensity of the incident light increased.
(ii) State the reason why the tube is evacuated.