past paper 1

Question

1.2

Two batteries of EMF 65 V and 50 V and internal resistance of 0,3 Ω and 0,6 Ω

respectively, are connected in parallel to supply a load resistance of 2,8 Ω.

Use Kirchhhoff’s laws to calculate the following:

1.2.1 The current supplied by each battery

1.2.2 The voltage across the load

 

1.3 The field coil of a motor has a resistance of 100 Ω at 250 C. By how much will the resistance increase if the motor attains a temperature of 1250 C when running. The temperature coefficient of resistance is 0,004 per degree C at 250 C.

 

2.1 A coil with 2000 turns of conductor wire with total cross-sectional area of 200 mm2 and a mean length per turn of 200 mm, has an inductance of 4 Henry.

Calculate the following:

2.1.1 The resistance of the winding if the specific resistance of the conductor is 2 micro-ohm metres

2.1.2 The average value of the EMF induced in the coil when a current of 10 A is reversed (i.e. to -10 A) in 20 seconds

 

3.1 A resistor of unknown value R is connected in parallel with a resistance of 180 Ω. This combination is connected in series with a resistor of 25 Ω. The circuit is then connected across a 280 V DC supply.

Calculate the following

3.1.1. The value of the resistor R when a 4 A current is drawn from the supply

3.1.2. The power dissipated in the circuit

 

Two capacitors connected in series have respective volt readings of 90 V and 30 V. If the total charge equals 900 μC, calculate the following:

3.2.1. The total capacitance

The value of each capacitor