CBSE Class 7 Science Chapter 14: Electric Current and its Effects NCERT Solutions

Here are the standard symbols used to represent the components of an electric circuit:

• Connecting Wire: A straight line.
• Switch in 'OFF' position: A break in the line with a lever not touching the contact point.
• Bulb: A circle with a cross or filament symbol inside.
• Cell: A combination of one long line (positive terminal) and one short line (negative terminal).
• Switch in 'ON' position: A continuous line where the lever touches the contact point, completing the circuit.
• Battery: A combination of two or more cell symbols connected in series (positive terminal of one to the negative terminal of the next).

Visual representation:

Connecting Wire: ———————

Switch (OFF): —○————

Bulb: (X) or (⊚)

Cell: + | - (Longer line is positive, shorter line is negative)

Switch (ON): —●————

Battery: + | - + | - (Multiple cells shown)

The provided image (Fig. 14.21) shows a simple electric circuit. To draw the circuit diagram, we use standard symbols for each component. Assuming Fig. 14.21 shows a battery, a switch, and a bulb connected by wires, the circuit diagram would represent these connections schematically.

A typical representation would include:

• A symbol for a battery (e.g., + | - + | -).
• A symbol for a switch (e.g., a break for OFF or a closed path for ON).
• A symbol for a bulb (e.g., (X)).
• Lines connecting these components to show the path of the current.

For example, if the switch is ON and the circuit is complete, the diagram would show the battery, switch, and bulb connected in a loop.

(Note: The actual diagram would depend on the specific configuration shown in Fig. 14.21, which is not fully rendered here. The solution provides the method to draw it.)

To create a battery from multiple cells, the positive terminal (+) of one cell must be connected to the negative terminal (-) of the adjacent cell. This series connection allows the voltage of the cells to add up.

Following this rule for the four cells shown in Fig. 14.22:

1. Connect the positive terminal of the first cell to the negative terminal of the second cell.
2. Connect the positive terminal of the second cell to the negative terminal of the third cell.
3. Connect the positive terminal of the third cell to the negative terminal of the fourth cell.

The free negative terminal of the first cell and the free positive terminal of the fourth cell will then serve as the terminals of the battery.

(Note: The diagram would visually demonstrate these connections, showing wires linking the appropriate terminals.)

If the bulb in the circuit shown in Fig. 14.23 does not glow, there is likely an issue with the circuit's completeness or the components themselves. Common problems include:

• Open Circuit: The switch might be in the 'OFF' position, or there could be a break in one of the connecting wires, preventing the electric current from flowing continuously.
• Incorrect Connections: The battery terminals might be connected incorrectly, or the bulb might not be properly seated in its holder.
• Faulty Components: The bulb could be fused (burnt out), or the battery might be discharged (run out of power).

To make the bulb glow, the necessary changes would be:

1. Ensure the switch is 'ON': If the switch is shown in the 'OFF' position (open), it needs to be moved to the 'ON' position (closed) to complete the circuit.
2. Check for breaks: Ensure all connecting wires are intact and properly connected, and that there are no gaps in the circuit path.
3. Verify Battery and Bulb: Confirm that the battery has sufficient charge and that the bulb is not fused.

Assuming the issue is an open switch, closing the switch would complete the circuit and allow the bulb to glow, provided the battery and bulb are functional.

(Note: The specific change required depends on the exact problem depicted in Fig. 14.23, which is not fully rendered here. The solution outlines the general troubleshooting steps.)