Lesson: Electric current and its Effects

Draw in your notebook the symbols to represent the following components of electrical circuits: connecting wires, switch in the ‘OFF’ position, bulb, cell, switch in the ‘ON’ position, and battery

Draw the circuit diagram to represent the circuit shown in the figure.

Figure below shows four cells fixed on a board. Draw lines to indicate how you will connect their terminals with wires to make a battery of four cells.

To make a battery of four cells, the positive terminal (+) of a cell must be connected to the negative terminal (-) of another cell, and this negative terminal should in turn be connected to the positive terminal of another cell, and so on and so forth.

The bulb in the circuit shown in the figure does not glow. Can you identify the problem? Make necessary changes in the circuit to make the bulb glow.

The positive terminal (+) of a battery must always be connected to the negative terminal (-) of another battery. Here the problem arises because two positive terminals are connected to each other, hence current will not flow through the bulb and the bulb will not glow.

The correct way to arrange the batteries and make the bulb glow is as follows:

Name any two effects of electric current.

Heating effect of electric current: When electric current passes through a metal wire, the latter gets heated. This property of electric current is made use of in various heating applications, such as, electric heaters, geysers, etc.

Magnetic effect of electric current: When electric current passes through a wire, a magnetic field is generated around it. This property has various uses, such as, electric bells, fans, power lifts, etc.

When the current is switched on through a wire, a compass needle kept nearby gets deflected from its north-south position. Explain.

When the current is switched on, the electric current that passes through the wire generates a magnetic field. A compass kept near this wire, will show deflection, as the magnetic field in the electric wire and the magnetic field in the compass would interact, causing deflection in the needle.

Will the compass needle show deflection when the switch in the circuit shown by the figure is closed?

No, there will be no deflection in the compass needle even when the switch is closed, as there are no batteries here to act as the source of electric current. Without any source, there would be no electric current, and thus no magnetic field would be generated in the wires.

Fill in the blanks:

(a)   Longer line in the symbol for a cell represents its ____________terminal.

(b)    The combination of two or more cells is called a ________.

(c)   When current is switched ‘on’ in a room heater, it____________.

(d)   The safety device based on the heating effect of electric current is called a ___________.

(a)   Longer line in the symbol for a cell represents its positive terminal.

(b)   The combination of two or more cells is called a battery.

(c)   When current is switched ‘on’ in a room heater, it gets hot.

(d)   The safety device based on the heating effect of electric current is called a fuse.

Mark ‘T’ if the statement is true and ‘F’ if it is false:

(a)   To make a battery of two cells, the negative terminal of one cell is connected to the negative terminal of the other cell. (T/F)

(b)   When the electric current through the fuse exceeds a certain limit, the fuse wire melts and breaks. (T/F)

(c)   An electromagnet does not attract a piece of iron. (T/F)

(d)   An electric bell has an electromagnet. (T/F)

(a)   To make a battery of two cells, the negative terminal of one cell is connected to the negative terminal of the other cell. (F)

(b)   When the electric current through the fuse exceeds a certain limit, the fuse wire melts and breaks. (T)

(c)   An electromagnet does not attract a piece of iron. (F)

(d)   An electric bell has an electromagnet. (T)

Do you think an electromagnet can be used for separating plastic bags from a garbage heap? Explain.

An electromagnet is a bar magnet and can attract only iron pieces. Plastic bags do not have magnetic properties; hence an electromagnet cannot separate them from a garbage heap.

An electrician is carrying out some repairs in your house. He wants to replace a fuse by a piece of wire. Would you agree? Give reasons for your response.

Fuses are used for safeguarding our electrical appliances and are made of special materials that melt rapidly and break the connection when a sudden large surge of electric current passes through it. If ordinary wires are used instead of proper fuse wires, there are chances of the wires getting overheated, causing a short circuit, and the appliances may catch fire. Therefore, it is advisable for the electrician to use standard fuse wires in order to avoid accidents.

Zubeda made an electric circuit using a cell holder shown in the figure, a switch and a bulb. When she put the switch in the ‘ON’ position, the bulb did not glow. Help Zubeda in identifying the possible defects in the circuit.

The possible defects in the circuit are:

·         The bulb may be a fused one

·         The cells/batteries may not be connected properly

·         The switch might be malfunctioning

·         The wire may have some loose connection

·         The cells may have exhausted

In the circuit shown in the figure.

(i)     Would any of the bulbs glow when the switch is in the ‘OFF’ position?

(ii)  What will be the order in which the bulbs A, B and C will glow when the switch is moved to the ‘ON’ position?

(i)     None of the three bulbs will glow when the switch is in the OFF position, as the circuit is incomplete and no electric current will flow through it.

(ii)  When the switch is moved to the 'ON' position, the circuit will be complete and there will be a flow of electric current. All of the bulbs will glow immediately at the same time.