Question

Janet installed a dimmer on the lights in her bedroom. She slid the dimmer switch, causing the resistance in the circuit to decrease. Assuming the voltage is constant, what affect will Janet’s actions have on the circuit? The voltage will increase from 120 to 240 volts. The lights will brighten. The current will decrease. The current will increase. The lights will dim.

Answer 1

Answer:

• The lights will brighten.
• The current will increase.

Explanation:

The question implies that the dimmer here is based on a resistor. For the dimmer to work properly, it needs to be connected to the lights in series. The total resistance of the series circuit is the sum of the resistance of

• the dimmer resistor, and
• the lights.

Reducing the resistance of the dimmer resistor will reduce the total resistance  of the circuit. The question states that voltage across the series circuit is "constant." There will not be a change in the voltage across the circuit. The voltage across the lights will increase but will not exceed the voltage of the power supply. The RMS voltage of power supply in the US is 120 volts. The voltage across the light will become closer to 120 volts. However, only reducing the resistance of the switch will not cause the voltage to exceed 120 volts.

$\displaystyle \rm Current = \frac{Voltage}{Resistance}$.

Resistance drops while voltage across the entire circuit stays the same. As a result, the current through the circuit will increase.

Current is the same for all appliances connected in series. The current in the lights will increase. Assume that the resistances of the lights stay the same,

$\displaystyle \rm Power = Current^{2} \times Resistance$.

Power dissipated in the lights will increase. More energy will be consumed to produce light in unit time. As a result, the lights will brighten.

Answer 2

Answer:

The lights will brighten.

The current will increase.

Explanation: