- A switch has a variable resistance that is nearly zero when closed and extremely large when open, and it is placed in series with the device it controls. Explain the effect the switch in Figure 21.43 has on current when open and when closed.
The effect of switch on current when open and closed.
Answer to Problem 1CQ
Current increases from zero to some constant value as the switch is closed from initial open state.
Explanation of Solution
Given:
Resistance of the switch when closed
Resistance of switch when open
Emf of the battery
Internal resistance of the battery
External resistance connected in series with battery
Current in the circuit when switch is closed
Current in the circuit when switch is open
Formula Used:
Equivalent resistance in series is given as
According to ohm's law
Calculation:
When the switch is open:
Equivalent resistance in series of the circuit given as
Using ohm's law, current in the circuit is given as
Since,
When the switch is closed:
Equivalent resistance in series of the circuit given as
Using ohm's law, current in the circuit is given as
Since
Clearly
Conclusion:
When switch is closed, there is some constant value of current in the circuit and when the circuit is open, there is no current in the circuit.
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