Electric Current and Its Effects Question Answers: NCERT Class 7 Science

Following are the symbles of the components of electric circuit are as follows:

No, the electromagnetic cannot be used for separating plastic bags from garbage heap because the electromagnets only attracts magnetic materials towards itself. Plastic bag is not a magnetic material, so electromagnet will not attract them.
 

No, the electrician will not be allowed to replace the fuse by piece of wire in the house. This is because a fuse filament cannot be made by any kind of wire. It must have a low melting point, so that it could melt easily and break, if the large amount of current is passes through it.  

The bulb is not glowing because of the two reasons. These are as follows:

1. One reason could be that may be the two cells are not connected properly. For the bulb to glow, the negative terminal of the one cell must be connected to the positive terminal of the another cell.
2. The another reason may be that the cell holder may not be tightly bound by the rubber band to keep the two cells in contact with each other. The circuit will not be complete and current will not flow through the circuit if the cells are not in contact with each other properly.

(i) No, the bulb will not glow when the switch is in the off position because the current will not pass through the circuit in the switch 'OFF' position.
(ii) When the switch is moved to the 'ON' postion, all bulbs will glow simultaneously because all the bulbs are connected to the same switch and same belt.

In the given circuit one terminal of the bulb is connected to the safety pin and another end is connected to the cell. Here, the circuit is not complete because the safety pin is not connected to the cell. Hence, safety pin shows off position of the switch.

In order to make battery, the positive terminal (+) of one cell should be connected to the (-) terminal of another cell and so on. Battery or we can say cell should be connected in series.

In this circuit, the bulb is not glowing because the cells are not connected properly. The cells should be connected like positive terminal of the one cell is connected to the negative terminal of another cell. To make the bulb glow cells should be connected properly.

The two main effects of electric current are as follows:

1. Heating effect of electric current: It may be defined as the electric current passes through the wire, it gets hot; it is known as the heating effect of the electric current. For example: heater, geezer, hair dryer etc.

2. Magnetic effect of electric current: It is also called as electromagnetic effect. When electric current is passed through a conducting wire then the magnetic field generate around it. It is called as the magnetic effect of the electric current. For example: Electric bell, electric motor, electric fan etc.

When the electric current is passed through a wire, it starts to behave like a magnet. So, when a compass needle is kept near a current carrying wire, it affects by the magnetic effect of electric current and show deflection from its north- south position.

No, the compass needle will not show any deflection when the switch is closed because the circuit does not have any source of current. The wire does not behave like a magnet in the absence of current.

(a) Positive                                                                                                                                                                                                                                      A cell have two terminals, one is positive and other is negative. The direction of current is from positive terminal to negative terminal.

(b) Battery
Battery is the combination of two or more cells in which positive terminal of the cell connected to the negative terminal of the another cell.

(c) Produces heat
It produces heat due to the heating effect of electric current.

(d) Fuse
Fuse limits the current in circuit and breaks the circuit, if current reaches its maximum limit.

(a) False
This statement is false because to make a battery the positive terminal of the cell should be connected to the negative terminal of the another cell.

(b) True                                                                                                                                                                                                                                               This statement is true because fuse is a safety device which is made up of a special material which have very low melting point. When current passes through a fuse in maximum amount then it melts quickly and break the circuit. 

(c) False
This statement is false because an electromagnet behaves like a magnet when we passes current through it. So it is obvious that it attracts iron pieces towards it.

(d) True
This statement is true because electric bell has a piece of iron which is bound by a coil. When we pass the current through the coil, it behaves like an electromagnet.