TRANSFORMERS MCQs SET 08

 TRANSFORMERS MCQs SET 08

1.Turns ratio of the transformer is directly proportional to ____________
a) Resistance ratio
b) Currents ratio
c) Voltage ratio
d) Not proportional to any terms
 

Answer: c 

Explanation: According to the voltage expression, emf induced in the primary is directly proportional to the change in the flux with respect to the time and number of turns of the primary winding. Similarly, for secondary winding.
 

2. Which of the following statement is correct regarding turns ratio?
a) Current ratio and turns ratio are inverse of each other
b) Current ratio is exactly same to the voltage ratio
c) Currents ratio is exactly same to the turns ratio
d) Voltage ratio and turns ratio are inverse of each other
 

Answer: a 

Explanation: Voltage ratio of transformer winding is exactly similar to the turns ratio of transformer, while voltage ratio and turns ratio is exactly inverse of the currents ratio. Hence, by knowing any of these quantities on can identify the type of transformer.
 

3. Which of the following is the expression for emf induced in primary with voltage applied to primary of an ideal transformer?
a) e=V
b) V= √2*e*cos ωt
c) e= √2*V*cos ωt
d) Cannot say
 

Answer: c 

Explanation: For an ideal transformer having a primary of N1 turns and a secondary of N2 turns on a common magnetic core. The voltage of the source to which the primary is connected is v = √2 V cos wt. while the secondary is initially assumed to be an open circuited. As a consequence, flux f is established in the core such that e = v = N1 dφ/dt.
 

4. Which of the following is the wrong expression?
a) i1N1=i2N2
b) i1v1=i2v2
c) i1N2=i2N1
d) v2N1=v1N2
 

Answer: c 

Explanation: According to the transformation ratio, current flowing through the transformer is inversely proportional to the number turns of winding and voltage applied across it. While, voltage applied is directly proportional to the number of turns.
 

5. For transformer given, turns ratio is equal to a, what will be the impedance of primary with respect to secondary?
a) a2 times the secondary impedance
b) a times secondary impedance
c) secondary impedance/a
d) secondary impedance/a2
 

Answer: d 

Explanation: The ratio of impedances on primary to the secondary is directly proportional to the inverse of square of turns ratio of transformer. Hence primary impedance to the secondary impedance ratio will be 1/ a2.
 

6. Power transformed in the ideal transformer with turns ratio a is _______
a) a2 times primary
b) a times primary
c) primary power/ a2
d) primary power
 

Answer: d 

Explanation: In an ideal transformer, voltages are transformed in the direct ratio of turns, currents in the inverse ratio and impedances in the direct ratio squared; while power and VA remain unaltered. Thus, primary power= secondary power.
 

7. For a transformer with primary turns 100, secondary turns 400, if 200 V is applied at primary we will get ___________
a) 80 V at secondary
b) 800 V at secondary
c) 1600 V at secondary
d) 3200 V at secondary
 

Answer: b 

Explanation: Voltage in the primary of the transformer will get modified in the transformer secondary, according to the number of turns. Thus, turns are modified with 4 times the primary, we’ll get 4 times higher voltage at secondary.
 

8. For a transformer with primary turns 400, secondary turns 100, if 20A current is flowing through primary, we will get ___________
a) 80A at secondary
b) 5A at secondary
c) 800A at secondary
d) 40A at secondary
 

Answer: a 

Explanation: Current in the primary of the transformer will get modified in the transformer secondary, according to the number of turns, in inverse proportion. Thus, turns are modified with 1/4 times the primary, we’ll get 4 times higher current at secondary.

9. When does transformer breath in?
a) load on it increases
b) load on it decreases
c) load remains constant
d) cannot be determined
 

Answer: b 

Explanation: Transformer in the low loading condition, also called extreme condition (lower temperature), oil inside contracts and then air is taken inside thus breath in to main via the balloon like structure through silica gel breather.
 

10. A transformer transforms ________________
a) voltage
b) current
c) power
d) frequency
 

Answer: c 

Explanation: Since, in a transformer voltage and current is changed according to the number of turns simultaneously, we call that power is transformed, though the magnitude remains same. Frequency is kept constant.