Rectification & Smoothing (CIE A Level Physics)

A technician is testing different bulbs using the half-wave rectifier in Fig. 1.1.

Fig. 1.1

The current I  passing through the ammeter in Fig. 1.1 varies with time t  according to the following equation:

The technician has the choice of three combinations (A, B, or C) of capacitors and resistors, as shown in Table 1.1:

Table 1.1

After using one particular combination, she notices the bulb being used is flickering. She recognises that this is a result of a highly fluctuating input current. 

State which combination she used and explain your answer.

The technician attaches an older lightbulb to the same combination as she used in part (a).

This older lightbulb operates by heating a tungsten filament, which then emits light as a result of its high temperature.

She notices this lightbulb flickers less than the previous, more modern lightbulb.

Suggest why the old lightbulb flickers less. 

The mean power supplied by the source of a.c. is 36 W.

Calculate the peak voltage across the bulb.

The next day, the technician sets up the equipment in Fig. 1.1 using resistor and capacitor combination B.

Calculate the potential difference across the plates of the capacitor, 0.20 ms after the potential difference across the bulb reaches its maximum value.

A sinusoidal alternating potential difference (p.d.) from a supply is rectified using a single diode.
The variation with time t of the rectified potential difference V is shown in Fig. 5.1.

Fig. 5.1

r.m.s. potential difference = .................................. V [2]

[1]

The alternating potential difference is rectified and smoothed using the circuit in Fig. 5.2.

Fig. 5.2

The capacitor has capacitance C of 85 μF and the resistor has resistance R.

The effect of the capacitor and the resistor is to produce a smoothed output potential difference V_OUT. The difference between maximum and minimum values of V_OUT is 2.0 V.

[3]

time = .................................... s [1]

R = ........................................ Ω [2]

An investigation into rectification used the circuit shown in Fig. 1.1.

Fig. 1.1

Sketch the expected variation of the output voltage with time for the circuit in Fig. 1.1.

A modification is made to the circuit to include a bridge recifier, as shown in Fig. 1.2.

Fig. 1.2

Sketch the expected variation of the output voltage with time for the circuit in Fig. 1.2.

A bridge rectifier consists of four ideal diodes, A, B, C and D, connected to an ac generator between the terminals X and Y, as shown in Fig. 1.3.

Fig. 1.3

On Fig. 1.3

The graph in Fig. 1.4 shows the output of an ac generator after undergoing half-wave rectification.

Fig. 1.4.

The load resistor has a resistance of 3.6 kΩ. Capacitors of capacitance 360 nF and 60 µF are available.

Determine which of the capacitors would be the most appropriate to smooth the output in Fig. 1.4.