1. The source of error in a Wheatstone bridge is due to _________
a) range of galvanometer used
b) type of the source of emf used
c) limiting errors of the three known resistances
d) balance condition
Explanation: The main source of error in a Wheatstone bridge is because of the limiting errors of the three known resistances. As a result very precise resistances are required with 1 % tolerance.
2. What is the main source of error in a null detector?
a) lower current detection ability
b) insufficient sensitivity of the null detector
c) wiring resistance
d) power dissipation
Explanation: Resistance of contact wires and power dissipation are some of the causes for error in a null detector. But insufficient sensitivity is the major source of error in a null detector such as a galvanometer
3. When current passes through the resistances in the Wheatstone bridge what happens?
a) voltage drop occurs
b) null detector burns
c) back emf is induced
d) temperature increases due to power dissipation
Explanation:Current flow through the resistances causes power dissipation i.e. I2R leading to an increase in the temperature. As the bridge consists of pure resistances, there is no back e.m.f induced
4. What is the effect of the increase in temperature on the resistance elements?
a) directly proportional
b) independent
c) inversely proportional
d) changes by a factor of 10
Explanation: Temperature affects resistance of the circuit. Resistance has a positive temperature coefficient and increases linearly with rise in temperature.
5. Heating effect in the Wheatstone bridge can be avoided by _________
a) using an expensive emf source
b) limiting current to a safe value
c) using heating sinks
d) immersing the setup in ice
Explanation: Heating effect can be eliminated by limiting the current through the circuit to a safe value and by calculating the power dissipation in the arms. Heat sinks are typically used in power electronic applications.
6. The main error when measuring low resistances is _________
a) power dissipation of the arms
b) voltage drop across the emf source
c) lead and contact resistance
d) current flowing through the circuit
Explanation:Voltage drop across the circuit along with power dissipation lead to errors in the measurement of low resistances. The resistance of leads and contacts of the external circuit adds to the values in the circuit. This is the main source of error while measuring low resistances.
7. How is thermal emf generated?
a) when current flows
b) when voltage is applied
c) when the null detector is connected
d) when dissimilar metals come in contact
Explanation: When dissimilar metals come into contact with each other in a galvanometer circuit, thermal emf is generated. Null detector is used for detecting the balance condition
8. Thermal emf can be prevented by _________
a) using more sensitive galvanometers
b) using similar metals
c) by separating the dissimilar metals
d) reducing the supply emf
Explanation: Thermal emf can be eliminated by making use of sensitive galvanometers consisting of copper coils and copper suspension systems. Dissimilar metals can’t be physically separated.
9. Wheatstone bridge is a __________
a) a.c. bridge
b) d.c. bridge
c) high voltage bridge
d) power dissipation bridge
Explanation: The Wheatstone bridge is a d.c. bridge that is used for the measurement of medium resistance. Schering bridge is used for measurement of high voltages. AC bridges comprise of Anderson bridge, Maxwell Bridge, etc.
10. Wheatstone bridge is used to measure resistance in the range of ________
a) 1Ω to a few megaohms
b) 10kΩ to a few megaohms
c) 100MΩ to a few gegaohms
d) 100Ω to a few teraohms
Explanation: Wheatstone bridge is the simplest form of bridge circuit. It is basically used for the measurement of medium resistances in the range of 1Ω to a few megaohms.