Question

# Pranati has set up a circuit as shown below. Which of the following could she put in the space marked 'X' to make the bulb glow brighter?

A

Bulb

B

Cell

C

Switch

D

Wire

Solution

## The correct option is B Cell To increase the brightness of the bulb in the given circuit, the current must be increased. According to Ohm's law, V=IR or I=VR Hence, to increase the current, either the potential difference has to be increased or the resistance has to be decreased in the circuit. Connecting a bulb at 'X' will increase the resistance, and hence will decrease the current in the circuit. If a cell is connected in the space marked as 'X' such that the positive terminal of the cell at 'X' is connected to the negative terminal of the cell present in the circuit, the potential difference in the circuit increases. Hence, the current in the circuit will increase. Therefore, a cell can be connected in the space 'X' to make the bulb glow brighter. However, connecting the cell in the opposite way may result in the bulb glowing dimmer or not glowing at all as the potential difference may decrease or will become zero. Connecting a switch in the space 'X' will change neither the potential difference nor the resistance. It can be used to break the circuit. It won't have any influence on the brightness of the bulb. Connecting a wire in the space does not result in the change in potential difference or the resistance (for all practical purposes). Hence, it won't have any influence on the brightness. Physics

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