MCQs on Electric Circuits

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01․ Which cell has the reversible chemical reaction?
Lead acid.
Mercury oxide.
Silver oxide.
Carbon Zinc.

A chemical reaction that can be reversed to its original state after it has reacted is called reversible chemical reaction. It happens only in Lead acid cells because mercury oxide, silver oxide, and carbon zinc cells cannot recharge again. Once the cell dried that is it and even if we connect with an external voltage source these cells cannot do any reaction. But, in the lead acid cells, once the cell has completely dried then if we give an external supply voltage, it reacts again and at the full charged condition it achieves the initial state. This is how we have differentiated the cells into primary and secondary types.

02․ The life of a lead acid battery is expected to be
6 months.
1 year.
2 to 5 years.
10 to 15 years.

The life of a lead acid battery is calculated in terms of charging / discharging cycles. The lead acid battery provides approximately 200 to 300 charging/discharging cycles. Also the life is short due to grid corrosion on the positive plate and a low voltage limit subjects to sulfation on the negative plate. Hence, the life of a lead acid battery is approximately in between 2 to 5 years.

03․ The capacity of a lead acid cell does not depends on its
rate of charge.
rate of discharge.
quantity of active material.

The rate of charge is used to denote that how fast the battery is getting charged and then the capacity is expressed in ampere-hours (AH) is the product of the current discharged and the duration of discharging time at a particular temperature. If the quantity of the active materials is more, then the capacity of the cell is more. Hence, the capacity of a lead acid cell does not depend on its rate of charge.

04․ Fillers in a lead acid battery are provided
to prevent flow of gases.
to facilitate flow of gases.
to recover acid loss through vapours.
all of above.

Lead-acid battery can produce explosive mixtures of hydrogen and oxygen gases when they are being charged. If ventilation is poor, the escaping hydrogen creates an explosive atmosphere around the battery. Always keep sparks, flames, burning cigarettes and other sources of ignition away from the battery recharging area because the gas can be ignited. The result of an explosion could be severe burns and/or fire. Hence, the filters in a lead acid battery are provided to facilitate the flow of gases.

05․ The term trickle charge is associated with
dry cell.
silver zinc battery.
lead acid battery.
nickel iron battery.

If we want to charge the lead acid battery, the constant voltage charging method is suitable. The trickle charging is one of a constant voltage charging system and that means charging a fully charged battery under no load at a rate which is equal to its self discharge rate. This can enable the battery to remain at fully charged level. That is why the trickle charging system is associated with lead acid battery. The silver zinc and nickel iron battery need a constant current source to charge them. The dry cell is a primary battery and that cannot be reused again.

06․ A 6 V lead acid battery has an internal resistance of 0.01 Ω. How much current will flow when the battery is short circuited?
1 A.
6 A.
100 A.
600 A.

In a battery, the short circuit current is the ratio of battery voltage to the internal resistance. Hence, Isc = 6 / 0.01 = 600 Amps.

07․ In a lead acid cell, hydrogen is liberated at
negative plate.
positive plate.
both plates.
none of the plates.

During the charging process, the battery cell cannot absorb all of the energy from the charging current supply. Through electrolysis principle, excess energy breaks down the water and it creates the hydrogen and oxygen gasses. The oxygen is liberated at the positive plates and the hydrogen at the negative.

08․ The lead acid cell should not never be discharged beyond
1.8 V.
1.9 V.
2 V.
2.1 V

Rather than a 100 percent depth of discharge, we have to charge the battery at 80 percent depth of discharge. The meaning is that only 80 percent of the available energy is being delivered and 20 percent remains in reserve. This kind of discharge method increases service life of the battery. The fully charged lead acid cell has 2.25 Volts. The 80% of this voltage is nearly to 1.8 Volts.

09․ The watt-hour efficiency of a lead acid cell varies between
20 to 35 %.
40 to 60 %.
70 to 80 %.
90 to 95 %.

Normally lead acid battery are having the watt-hour efficiency between 70 to 80%.

10․ The internal resistance of lead acid cell is _______________ that of Edison cell.
less than.
more than.
equal to.
none of above.

The Edison cell is nothing but the nickel battery. In the nickel battery, the positive and negative plates are in the form of nickel plated steel tubes that filled with Ni(OH)4. Due to the presence of nickel, it increases the internal resistance of the cell because the nickel has higher resistance in nature.