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Q22. The network shown in Fig Q1 is for sensing temperature.

(a) Calculate the value of the sensing element Rx so that the meter will read full scale deflection (FSD) of 1 mA.

(b) The meter becomes unserviceable and is replaced with one of the same resistance but full scale deflection 2 mA.

Calculate the value to which the 200Ω resistor will have to be changed to enable the meter to continue reading FSD.

Q7. The network shown in Fig Q 1 is for sensing temperature.

(a) Calculate the value of the sensing element 'R' so that the meter will read full scale deflection (FSD) of 1 mA in the direction shown.

(b) Calculate the value to which the 200 Ω resistor will have to be changed if the meter becomes unserviceable and has to replace by one of the same resistance but of 2 mA FSD and the meter is still to read full scale deflection.

Q4. A relay coil has a resistance of 200 Ω and the current required to operate the relay is 150 mA.

When the coil is connected to 50 V d.c. it takes 40 ms to operate. Calculate EACH of the following:

(a) The steady state relay current;

(b) The time constant for the coil;

(c) The inductance of the coil.

(d) To increase the operating time of the relay, a 50 Ω resistor is connected in series with the coil.

Calculate the new operating time for the relay.

Q2. A coil of resistance R and inductance L is connected to a 50 Hz supply and draws a current at a power factor of 0.8 lag. If a capacitor of 100 μF is now connected in series with the coil the circuit draws the same current but at a power factor of0.8 lead. Calculate EACH of the following:

(a) The inductance of the coil;

(b) The resistance of the coil.

If the voltage measured across the capacitor is 36 V, determine EACH of the following:

(c) The current in the circuit;

(d) The supply voltage.

Q5. A 440 V /110 V single phase step down transformer is rated at 60 kV A full load output. The iron loss is 4 kW and the copper loss at full load is 6 kW. Calculate EACH of the following:

(a) The kVA output at which maximum efficiency will be achieved;

(b) The efficiency at 50 kW output and 0.85 p.f.