q2 past year paper

Question

Q1 1.1. three capacitors of 2 microfarads, 4 microfarads and 6 microfarads respectively are connected in series a 100 volt supply. Calculate: a. the total capacitance b. the pd across each capacitor. 1.2. define farad 1.3. two capacitors of 3 microfarads and 6 microfarads respectively are connected in series. This combination is then connected in parallel with a 4 microfarads capacitor across a 200 volts DC supply. Calculate the total change, capacitance, the charge across the series capacitors and potential difference (PD) across each of the series capacitors. Q2 2.1. name three principle sources of EMF. 2.2. a battery having EMF of 50 volts and internal resistance of 0,3 ohms is connected in parallel with a direct-current generator of EMF 60 Volts and internal resistance of 0,4 ohms. The combination is used to supply a load having a resistance of 10,6 ohms. Use Kirchoff’s theorem to determine: 2.2.1. the value and direction of the current through the battery 2.2.2. the value and direction of the current through the generator 2.2.3. the potential difference across the load Q3 An aluminum conductor of unknown length with a voltage of 75V is connected in parallel with a copper conductor with same length. When a current of 10A is passed combination, it is found that Determine: 3.1. the length of the copper conductor if the resistively of copper is 0,017 micro-ohm meters and that of aluminum is 2,5mm. micro-ohm meters. 3.2. the current through the copper conductor is 2,5A. the diameter of the aluminum is 2,5mm. the resistance and the diameter of the copper conductor. Q4 4.1. the field coils of motor have a resistance of 50 ohms at 10 degrees Celsius. After a run at full load, the resistance increases to 100 ohms and the temperature of the coils to 201 degrees Celsius. Calculate the temperature coefficient of resistance at 0 degrees Celsius. 4.2. the field-coil of motor has a resistance of 100 ohms at 15 degrees Celsius. By how much will the resistance increase if the motor reaches a temperature of 65 degrees Celsius when running? Take the temperature coefficient of resistance to be 0,004 per degrees Celsius at 15 degrees Celsius. 4.3. difference between positive and negative coefficient of resistance.

Answer 1

(3.2)

Step 1:

Find the resistance of copper conductor.

Specific resistivity of the copper .

The length of copper conductor l  is 1.96 km.

The diameter of the copper wire is 1.1902 mm.    [From (3.1)]

Resistance offered by copper wire is .

Resistance of the copper conductor is 30 ohms.

Solution :

(a) Resistance of the copper conductor is 30 ohms.

(b) The diameter of the copper wire is 1.1902 mm.