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Q1— Section header —
1.1Germanium has an atomic number of 32. State how many electrons are in the:
1.1.1First shell (1\
1.1.2Second shell (1\
1.1.3Third shell (1\
1.1.4Fourth shell (1\
1.1.5Valency shell (1\
1.2Complete the following sentences by writing only the missing word or words next to the question number (1.2.1
1.2.5\n the ANSWER BOOK.
1.2.2Th
1.2.3If the cross sectiona l area of a conductor is halved and the length
1.2.5
1.3Calculate the resistance of a copper conductor with a length of 1 000 m and a cross sectional area of 35 mm . T
1.4Wh at effect does an increase in temperature have on the resistance of insulating materials? (2\ [15]15
Q2— Section header —
2.1Explain the term magnetomotive force (2\
2.2Calculate the magnitude of flux produced by a coil when the flux density is 180 T and the area of the magnetic circuit is 400 mm (3\
2.3State Lenz' s l aw (2\
2.4Explain the principle of electromagnetic induction (2\ (12041003\
2.5A coil with an effective length of 250 mm moves through a magne tic field of 0,008 Wb/m at a velocity of 50 m/s. Calculate:
2.5.1The maximum emf in the coil
2.5.2
2.6Explain the operation of a n electric bell (4\
2.7State the screw rule that applies to magnetic circuits. (3\ [20]20
Q3— Section header —
3.1then connected in series with an unknown resistor Rx. The c ircuit is connected across a 12 V DC supply and a current of 2 A is drawn from the supply. Calculate:
3.1.1The unknown resistance Rx (5\
3.1.2(4\
3.2in
Q3— Section header —
3.3
3.4
3.4.1 Series (3\
3.4.2 Parallel (2\
3.4.3What can you conclude from the above res ults? (1\
3.5State T WO ways in which cells can be grouped to form a battery. (12041003\
3.7A single phase load draws a current of 3 A from a 220 V supply at a power factor of 0,75. Determine the real power drawn by the load. (2\
3.8Explain each of the following terms relating to a three phase system: 3.
3.830
Q4— Section header —
4.1Explain the working of deflecting device. (2\
4.2Give THREE disadvantages of a dynamometer type instrument. (3\
4.3Explain how to measure the res istance of a resistor in a circuit using a digital multimeter. List the details of each step clearly. (5\
4.4A moving coil instrument has a resistance of 10 it takes 25 mA to produce full scale deflection. Calculate the values of the resistors to be used with the instrument so that it will be able to measure
4.4.1Voltage up to 150 V (2\
4.4.2urrent of 20 A (3\ [15]15
3.6
5.1Refer to FIGURE 2 and answer the questions FIGURE 2
5.1.1Identify FIGURE 2. (1\
5.1.2Explain the energy conversion taking place in FIGURE 2. (2\
5.2Explain the term wave winding as applicable to DC machines. (2\
5.3Briefly explain each of the following c omponents found in a DC machine:
5.3.1Frame (1\
5.3.2Stator (1\
5.3.3Armature core (2\
5.4DC motors are classified as series, shunt and compound depending on the connections of the fi eld windings with the armature and supply.
5.4.1State TWO characteristics of a series motor. (2\
5.4.2Give TWO applications of a compound wound motor. (2
5.5Explain a self excited generator. (2\
5.6The fu ll load armature current o f a DC motor is 40 A and the armature resistance is 0,185 Calculate the back emf induced in the armature if the supply voltage is 220 V
5.7series wound generator delivers 30 A at 330 V to the load. If the series field and ar and 0,05 respectively, calculate th e magnitude of the generated emf.