MCQs on Electric Circuits

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01․ For closer tolerance which of the following capacitors is usually preferred?
Paper capacitor.
Ceramic disc capacitor.
Mica capacitor.
None of them.

The flow of electrons in a dielectric medium causes the voltage variation in it by charging and discharging principle. During the working time, the voltage variation affects the value of capacitance. The amount of capacitance variation with change in voltage is known as tolerance of a capacitor. In mica, the change in capacitance with the voltage change is always less in nature. Hence, the tolerance value of mica capacitor is less than other above mentioned type.

02․ Mica capacitor are characterised by all of following except
stable operation.
accurate value.
low leakage reactance.
low losses.

Internal construction of the mica capacitor has direct contact to the electrodes on both ends. This contact keeps all current paths very short. The design behaves like a large number of individual capacitors are connected in parallel, thus reducing the internal ohmic losses. This results in low ohmic losses and a low leakage reactance. Hence, the mica capacitor is not characterized by this low leakage reactance because it is always low.

03․ Paper condenser is
always polarised.
electrolytic capacitor.
usually fixed value.
a variable condenser.

There is no electrolytic oxide for making the dielectric medium because oil impregnated paper between the metallic plates can act as a dielectric medium. So, it is not an electrolytic capacitor. Once the fabrication process is done in the paper condenser, then we cannot be able to change the value of capacitance. So, it is usually a fixed value capacitor.

04․ Which of following capacitors has relatively shorter shelf life?
both (B) and (C) above.

The electrolytic capacitors have less shelf life, due to the following chemical reactions. If the electrolytic capacitor is exposed to high temperature atmosphere, sealing material can be degraded to lower sealing power and electrolyte can be lost due to dissipation. When aluminum electrolytic capacitor is stored the charge for a long time without electric input, leakage current may increase and capacitance may decrease. One of the reasons why leakage current increases is the penetration of electrolyte into defects in the place of the oxide film's diffusion of oxygen and it may consume bulk electrolyte.

05․ The breakdown voltage for paper capacitor is usually
20 to 60 volts.
200 to 1600 volts.
2000 to 3000 volts.
more than 10000 volts.

The breakdown voltage of a capacitor depends on the dielectric strength of the dielectric medium. The dielectric strength of the paper material is not less and it is not too more. It has a moderate dielectric strength.

06․ Which of following capacitor will have least value of breakdown voltage?

The dielectric strength of the electrolytic acid is very less than the other type of dielectric materials. Hence, it has least value of breakdown voltage.

07․ Which of the following capacitors is marked for polarity?

The electrolytic capacitors work only on DC power supply. So, the polarity is marked near the terminal ends of the electrolytic capacitor.

08․ A gang condenser is a
variable capacitor.
polarised capacitor.
ceramic capacitor.
all of above.

The gang condenser is nothing but number of single capacitors that might be connected depending on the requirement. Whenever we need to have more capacitance, then the capacitors can be connected in parallel one by one. So, it is a variable capacitor. Usually, this type of capacitor is used in power factor correction.

09․ The capacity of a cell is measured in

The capacity of the cell is measured by the discharging at a constant current until it fully drains out for that particular time. Hence, the capacity of the cell/battery is measured by the Ampere-hour rating.

10․ The storage battery generally used in electric power station is
nickel-cadmium battery
zinc-carbon battery.
lead-acid battery.
none of above.

Deep-cycle lead acid (DCLA) battery provide a steady current over a long time period and these are all connected together to form a battery bank. The technology of lead acid battery is uncomplicated and manufacturing costs are low compared to other type of battery. So, it is cost effective and it has good discharging characteristics.