1. What is the effect of load and contact resistance in Kelvin bridge?
a) independent
b) fully dependent
c) partially dependent
d) depends on the resistance value
Explanation: Effect of contact and lead resistances are completely eliminated in a Kelvin bridge as they don’t appear in the balance equation. Hence the Kelvin bridge is independent of the load and contact resistances
2. The relation between ratio of resistance arms and ratio of resistance arms of second bridge is _________
a) unequal
b) equal
c) twice
d) one forth
Explanation: The relation between the ratio of the resistances of resistance arm and second resistance arm is equal for balance condition.
3. Why Kelvin bridge is used for measurement of low resistance?
a) due to e.m.f source used
b) due to a large current flow
c) due to contact and lead resistance
d) due to power dissipation across the circuit
Explanation: While measuring very low resistances the contact and lead resistances cause significant errors in the value of the measured resistance. As a result Kelvin bridge is used for measurement of low resistances.
4. What is the condition to achieve a high sensitivity in a Kelvin bridge?
a) low voltage
b) high power
c) medium resistance
d) high current
Explanation: The condition to achieve a high sensitivity in a Kelvin bridge is that the measuring current should be high enough so as to sensitize the null detector
5. Kelvin bridge can be calibrated to read _________
a) inductance and Quality factor value
b) capacitance only
c) power and voltage
d) current and frequency
Explanation: In its basic form a Kelvin bridge is used for the measurement of low resistance. A Kelvin bridge can be used for the measurement of inductance and Quality factor value through calibration.
6. Why can’t a Kelvin bridge be used for the measurement of low Quality factor value?
a) due to thermoelectric effect
b) due to balance problem
c) due to the dull detector used
d) due to temperature
Explanation: A Kelvin bridge can be used for the measurement of high Quality factor values. Due to bridge imbalance problem, Kelvin bridge can’t be used for measuring low Quality factor values.
7.High resistances are of the order of __________
a) 0.1 Mῼ
b) 10 mῼ
c) 1 kῼ
d) 10 Gῼ
Explanation: Resistances of the order of 0.1 Mῼ and above are known as high resistances. Resistance values upto 1 ῼ are known as low resistances. Resistances upto a few kῼ are known as medium resistances
8. Megger is a ________
a) source of e.m.f
b) source to measure high resistance
c) type of a null detector
d) current carrier
Explanation: Megger is a portable instrument to measure high resistances.
9. Megger is also used for ________
a) providing additional e.m.f
b) bridge balance
c) testing insulation resistance
d) controlling the temperature
Explanation: A null detector is used to balance the bridge. Additional e.m.f can be provided to a circuit by increasing the magnitude of the voltage source. Megger is used for testing the insulation resistance of cables.
10. Megger works on the principle of ________
a) kirchhoff’s current laws
b) ohm’s law
c) gauss’s law
d) electromagnetic induction
Explanation: Ohm’s law is applicable to only purely resistive circuits which are based on the linearity principle. Megger basically works on the principle of electromagnetic induction.