ELECTRODYNAMICS: ELECTRICAL MACHINES QUESTIONS AND ANSWERS

ELECTRODYNAMICS: ELECTRICAL MACHINES QUESTIONS AND ANSWERS Electrical machines are at the heart of modern society, powering everything from household appliances to industrial machinery. Understanding the principles of electrodynamics is essential for engineers and enthusiasts alike. In this page, we’ll explore some common questions and answers related to electrical machines and their underlying electromechanical principles.

Activity 1
A simplified sketch of a generator is shown below.

1. Is the output voltage AC or DC? Give a reason for your answer. (2)
2. What type of energy conversion takes place in the above generator? (2)
3. State TWO effects on the output voltage if the coil is made to turn faster. (2)
4. What is the position of the coil relative to the magnetic field when the output voltage is a maximum? (1)
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Activity 2
Lights in most households are connected in parallel, as shown in the simplified circuit below. Two light bulbs rated at 100 W; 220 V and 60 W; 220 V respectively are connected to an AC source of rms value 220 V. The fuse in the circuit can allow a maximum current of 10 A.

1. Calculate the peak voltage of the source. (3)
2. Calculate the resistance of the 100 W light bulb when operating at optimal conditions. (3)
3. An electric iron, with a power rating of 2 200 W, is now connected across points a and b. Explain, with the aid of a calculation, why this is not advisable. (5)
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Activity 3
The essential components of a simplified DC motor are shown in the diagram below.

When the motor is functioning, the coil rotates in a clockwise direction as shown.

1. Write down the function of each of the following components:
   1. Split-ring commutator (1)
   2. Brushes (1)
2. What is the direction of the conventional current in the part of the coil labeled AB? Write down only FROM A TO B or FROM B TO A. (1)
3. Will the coil experience a maximum or minimum turning effect (torque) if the coil is in the position as shown in the diagram above? (1)
4. State ONE way in which this turning effect (torque) can be increased. (1)
5. Alternating current (AC) is used for the long-distance transmission of electricity.
   Give a reason why AC is preferred over DC for long-distance transmission of electricity. (2)
6. An electrical appliance with a power rating of 2 000 W is connected to a 230 V rms household mains supply.
   Calculate the:
   1. Peak (maximum) voltage (3)
   2. rms current passing through the appliance (3)
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Activity 4
Electric motors are important components of many modern electrical appliances. AC motors are used in washing machines and vacuum cleaners, and DC motors are used in toys and some tools.

1. What energy conversion takes place in electric motors? (2)
2. What is the essential difference in the design between DC motors and AC motors? (4)
3. List THREE ways in which the efficiency of the motor can be improved. (3)
4. Consider the diagram. The conventional current direction is indicated by the arrows.
   1. In which direction (clockwise or anti-clockwise) will the coiled armature rotate if the switch is closed? (1)
   2. Why does the armature continue moving in the same direction once it has reached the vertical position? (2)
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Activity 5
In the circuit the AC source delivers alternating voltages at audio frequency to the speaker.

1. What is the peak voltage that the source can deliver? (3)
2. Calculate the average power delivered to the speaker. (7)
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