Question

A student wires a $1$ device which is fused at 1A (it is cannot operate at currents above 1A) in series with a 6V battery. The only other electrical equipment available to this students is a large number of $2$ resistors.
How should she connect the $2$ ohm resistors to ensure the correct operation of the light bulb?

• A. The student can wire three $2$ ohm resistors in series with the device.
• B. The student can wire two $2$ ohm resistors in parallel and then wire this combination in series with the device.
• C. The student can wire two $2$ ohm resistors in parallel and then wire this combination in series with the device and with another $2$ resistor.
• D. The student can wire two $2$ ohm resistors in parallel and then wire this combination in series with the device and with two $2$ resistors.
• E. The student can wire three $2$ ohm resistors in parallel and then wire this combination in series with the device and with another $2$ resistor.

Answer 1

The correct option is A The student can wire three $2$ ohm resistors in series with the device.

Let the student wire three $2\Omega$ resistors in series and then wire this combination in series with the device as shown in the figure.

Thus equivalent resistance of the circuit $R_{eq}=2+2+2=6$ $\Omega$

$\therefore$ Current flowing through the device $I=\frac{V}{R_{eq}}=\frac{6}{6}=1$ A

Hence the device is safe.