Electric Current and its Effects (NCERT Solutions, Class 7)

(1) 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.

Ans-The Symbols of required components of electrical circuits are given below:

schoolhelpbygunjan.wordpress.com | Electric current and its effects | Diagram | Symbols for some electric circuit components | NCERT | Class 7(2) Draw the circuit diagram to represent the circuit shown in figure given below:

Electric current and its effect, Q 1,NCERT, class 7

Ans- The circuit diagram of given figure is shown below:

Electric current and its effects, diagram, open curcit,bulb is not getting hot, NCERT, class 7

(3) 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.

Electric current and its effect, Q 3,NCERT, class 7

Ans– Connections of wire of four cells are shown below:

Electric current and its effect, diagram, electric curcit, NCERT, class 7

(4) The bulb in the circuit shown in fig given below does not glow. Can you identify the problem? Make necessary changes in the circuit to make the bulb glow.

Electric current and its effect, Q 4,NCERT, class 7

Ans- The bulb in the figure is not glowing because cells are connected in wrong position. Positive terminal of one cell is connected to positive terminal of another cell. The correct circuit is shown below:

Electric current and its effect, A 4,NCERT, class 7

(5) Name any two effects of electric current.

Ans-

(i) Heating effect of electric current

(ii)Magnetic Effect of Electric Current

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

Ans- When the current is switched on through a wire, a compass needle kept nearby gets deflected from its north – south position.  It means, when the electric current passes through the wire, it behaves like a magnet and whenever we bring a magnet near to compass needle it deflected from its north south position. This is the magnetic effect of the electric current.

(7) Will the compass needle show deflection when the switch in the circuit shown by figure given below is closed?

 

Electric current and its effect, Q 7,NCERT, class 7

Ans- Yes, compass needle will show deflection when the switch in figure is closed. In closed circuit current flows. So, coil will turn to electromagnet. Thus, magnetic effect will be shown by needle. The closed circuit of given figure is showing below.

(8) 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 ______.

Ans-

(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 produces heat.

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

 (9) Mark’T’ if the statement is true and ‘F’ I fit 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.

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

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

(d) An electric bell has an electromagnet.         

 Ans-

(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      

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

Ans- No, an electromagnet can not be used for separating plastic bags from a garbage heap because an electromagnet attracts only iron.

(11) 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.

Ans-No, it is not good idea to replace fuse by a piece of wire because wires have high melting points. So, they will not melt and break if electric current exceeds the limit. It will cause an accident. Thus, fuse filament of low melting point is good instead of wire.

(12) Zubeda made an electric circuit using a cell holder in fig given below, 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.

Ans- Zubeda should check given possibilities of not glowing bulb-

(i) Rubber band can be not tight to hold cells in contact.

(ii) Cells terminals can be connected wrong.  Positive terminal of one cell should be connected to the negative terminal of the other cell.

(13) In the circuit shown in figure below:

Electric current and its effect, Q 13,NCERT, class 7

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

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

Ans-

(i)No, any of the bulbs will not glow when the switch is in ‘OFF’ position. Because there will be no current in the circuit. So, no heating effect of the current will happen.

(ii)When the switch is moved to the ‘ON’ position the bulbs A, B, and C will glow at same time because these are connected to the same switch and battery.

Helping Topics

Electrical Current and its Effects

Practice sheet, class 7

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