Question

Complete the drawing shown in Fig. 9.14 to indicate where the free ends of the two wires should be joined to make the bulb glow

Answer 1

To understand the functioning of an electric circuit with a switch and a bulb, let’s consider the following scenario.

Initially, the connection is incomplete because one end of the cell is not connected to the switch, and consequently, the bulb does not light up. In an electric circuit, the flow of current is necessary to light the bulb. The current flows from the positive terminal of the cell, through the wires, the switch, and the bulb, and then returns to the negative terminal of the cell. This continuous path allows electrons to flow, providing the necessary energy to light the bulb.

 Steps to Complete the Circuit

1. Identifying the Components:
  - Cell: Provides the electrical energy for the circuit.
  - Switch: Acts as a control device to open or close the circuit.
  - Bulb: The load that will convert electrical energy into light.

2. Current Flow:
  - In a closed circuit, electrons flow from the negative terminal of the cell to the positive terminal through the various components.
  - If any part of this path is broken, the current cannot flow, and the bulb will not light up.

3. Incomplete Circuit:
  - Initially, the circuit is incomplete because one end of the cell is not connected to the switch. This means there is a break in the path, preventing current from flowing through the circuit and thus, the bulb does not light up.

Completing the Circuit

To make the bulb glow, we need to complete the circuit. Here are the steps to do so:

1. Connect the End of the Cell to the Switch:
  - Take a wire and connect it from the free end of the cell to one terminal of the switch.
  
2. Connect the Switch to the Bulb:
  - Then, connect another wire from the other terminal of the switch to one terminal of the bulb.

3. Complete the Return Path:
  - Finally, connect a wire from the other terminal of the bulb back to the remaining terminal of the cell.

Closing the Switch

Once the connections are made, the switch can be used to control the flow of current:

1. Switch Open:
  - When the switch is open, there is a break in the circuit, and no current flows. Consequently, the bulb remains off.

2. Switch Closed:
  - When the switch is closed, it completes the path for the current to flow. Electrons move from the negative terminal of the cell, through the closed switch, pass through the bulb, and return to the positive terminal of the cell.

Result

With the switch closed, the circuit is complete. The current flows through the circuit, and the bulb lights up as shown in the figure. This demonstrates the fundamental principle of an electric circuit where a complete and unbroken path is necessary for the current to flow and power a device such as a bulb.

By ensuring all components are properly connected, and the switch is closed, the circuit allows the electrons to flow, providing the energy needed to make the bulb glow brightly.