# C&G 2357 Unit 309 Mock Exam

16. What is EMF?

a) electro-motive force

b) electron-motive force

c) electro-magnetic force

d) electron-magnetic force

17. What unit is used to describe the 'work' taken to 'push' electrons around a circuit?

a) Volts

b) Watts

c) Coulombs

d) Joules

18. What safety must be acknowledged when working with capacitors?

a) They are heavy

b) They can store a charge so present a shock hazard

c) They contain liquids so must be mounted upright

d) They only work on AC

19. What effect does an inductor have on an AC circuit?

a) Decreases its resistance

b) Converts it to DC

c) No effect

d) Sets up opposing current

20. How is power calculated?

a) Volts multiplied by resistance

b) Volts multiplied by current squared

c) Volts squared divided by resistance

d) Current squared multiplied by resistance squared

21. What material are 'brushes' - used in AC and DC generators and motors made from?

a) Brass

b) Rubber

c) Copper

d) Carbon

22. What is the unit of measure for 'Magnetic Flux' ?

a) Weber

b) Farad

c) Henry

d) Tesla

23. What are eddy current losses?

a) Heat loss caused by the windings

b) Magnetic loss in the transformer

c) Degradation of the iron core

d) Induced currents are retained in the iron core

24. A 10 microFarad capacitor is connected to a 240v 50Hz supply. Calculate the capacitive reactance?

a) 400 ohms

b) 228 ohms

c) 375 ohms

d) 318 ohms

25. A 3kW immersion heater is connected to a 230v AC supply. calculate the current drawn from the supply.

a) 13A

b) 14A

c) 12A

d) 10A

26. By which method is power factor improved in an AC circuit?

a) Fitting an inductor is parallel with the load

b) Fitting an inductor is series with the load

c) Fitting a capacitor is parallel with the load

d) Fitting a capacitor is series with the load

27. What is the voltage level for SELV transformer?

a) Less than 25v AC

b) Between 50v and 230v AC

c) Less than 120v AC

d) Less than 50v AC

28. What does AC mean?

a) Actual Current

b) Amplitude Current

c) Attenuated Current

d) Alternating Current

29. Which losses in a transformer can be reduced if the core material is carefully chosen?

a) Copper losses

b) Iron losses

c) Eddy current losses

d) Hysteresis losses

30. What determines the speed control of a synchronous motor?

a) Rotor construction material

b) Current

c) Voltage

d) Frequency