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

Solution: To represent electrical circuits accurately, specific symbols are used for each component. Here are the standard symbols:

• Cell: A single long line (positive terminal) and a shorter parallel line (negative terminal). Symbol: $+$ | $-$
• Battery: A combination of two or more cells connected in series. Symbol: A series of long and short parallel lines.
• Switch in 'OFF' position: An open switch, showing a break in the circuit. Symbol: $\perp$
• Switch in 'ON' position: A closed switch, showing a continuous path for current. Symbol: $\perp$ (with the switch arm touching the contact)
• Bulb: A circle with a cross or a filament symbol inside. Symbol: $␡$
• Connecting Wire: A straight line representing the wire. Symbol: —

Students should draw these symbols neatly in their notebooks as per the standard conventions.

Solution: The provided image (Fig. 14.21) shows a simple electric circuit. To draw the circuit diagram, we need to represent each component using its standard symbol and connect them appropriately.

The circuit consists of:

• A battery (represented by multiple cells connected in series).
• A switch (shown in the 'ON' position, indicating a closed circuit).
• A bulb (which will glow when current flows through it).
• Connecting wires.

The circuit diagram will show these components connected in a loop. The positive terminal of the battery connects to the switch, the switch connects to the bulb, and the bulb connects back to the negative terminal of the battery, forming a closed path for the electric current.

(Note: The actual drawing of the circuit diagram would be based on the visual representation in Fig. 14.21, which is not fully rendered here. The description outlines the process of creating it.)

Solution: To construct a battery from multiple cells, the cells must be connected in series. This means the positive terminal (+) of one cell is connected to the negative terminal (-) of the adjacent cell. This process is repeated for all the cells.

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 actual connection lines would be drawn on the image provided in Fig. 14.22.)

Solution: If the bulb in the circuit shown in Fig. 14.23 does not glow, the most likely problem is that the switch is in the 'OFF' position, or there is a break in the circuit. In the 'OFF' position, the switch opens the circuit, preventing the flow of electric current from the battery to the bulb.

To make the bulb glow:

1. Identify the switch in the circuit diagram.
2. Ensure the switch is moved to the 'ON' position. This closes the circuit, allowing current to flow from the battery, through the bulb, and back to the battery.

If the switch is already in the 'ON' position and the bulb still does not glow, other potential issues could be a loose connection, a faulty bulb (fused), or a dead battery. However, based on the typical representation of such problems, the switch position is the primary issue to address.

(Note: The specific changes would involve altering the switch's state in the diagram of Fig. 14.23.)