Page 600 - Basic Electrical Engineering

11. A transformer has 350 primary turns and 1050 secondary turns. The primary winding is
connected across a 230 V, 50 Hz supply. The induced EMF in the secondary will be

a. 690 V, 50 Hz
b. 690 V, 100 Hz
c. 690 V, 150 Hz
d. 115 V, 50 Hz.

12. The rating of a transformer is expressed in

a. kW
b. kVA
c. kWh
d. cos ϕ.

13. The ampere-turns balance equation for a transformer on load can be expressed as

a. I N = I N
1 1
2 2
b. I N >> I N
2 2
1 1
c. I N = I N
2 2
1 1
d. I N < I N .
2 2
1 1
14. Which of the following characteristic assumptions for an ideal transformer are true?
a. Coupling coefficient between the windings is unity
b. There are absolutely no core and copper losses
c. The core is made up material having infinite permeability
d. All the characteristics as in (a), (b), and (c).

15. The EMF equation for a transformer is

2
a. E = 4.44 ϕ f N
b. E = 4.44 ϕ fN
2
c. E = 4.44 ϕ f N
d. E = 4.44 ϕ f N.
n
16. Which of the following statements is true for a transformer?

a. A transformer is an energy conversion device
b. A transformer changes the voltage and frequency from one level to the other
c. A transformer is a static variable frequency device
d. A transformer transforms or changes voltage level of energy utilization keeping the
frequency constant.

17. Which of the following effects will the secondary load current of a transformer will have on
the main flux created by the magnetizing current?