Science 3 Marks Question

One of the reasons may be that the rubber band used in the cell holder may not be tight enough to keep the two cells in contact with each other. If the cells are not in proper contact with each other, then the circuit will not be complete and current will not flow through the circuit. Hence, the bulb will not glow.

The other reason may be that the two cells are not connected properly. The negative terminal of one cell must be connected to the positive terminal of the other cell.

Some of the questions which may arise in our mind are as follows:

1. Why does the iron nail attract the pins placed near its ends?
2. On disconnecting the circuit, why pins get detached from the iron nail?
3. What will happen if we use some other material like wood or straw in place of iron nail?

To make a battery, the negative terminal of one cell must be connected to the positive terminal of the next cell. The wire indicates the manner in which the given cells should be connected with each other, as shown in the following figure.

Overloading can be avoided if too many appliances are not connected to a single socket. Short circuiting is a name given to a situation in which the live and the neutral wires accidently come in contact. Electric fuse is a safety device. When a short circuit takes place or when overloading takes place, then the current becomes large and heats the fuse wire too much and thus, it gets melted and circuit breaks which prevents the damage of the wiring and electrical appliances.

1. No, the amount of heat produced in both the wires will be different because amount of heat produced in a wire on passing electric current depends on the length of wire and here length is different for both the wires.
2. No, the amount of heat produced in the wire of same length but different thickness cannot be same because amount of heat produced in a wire also depends on the thickness of the wire.

There is a maximum limit on the current which can safely flow through a circuit. If by accident the current exceeds this safe limit, the wires may become overheated and may cause fire. In order to prevent this, in all buildings fuses are inserted in all electrical circuits. If a proper fuse is there in the circuit, it will blow off and break the circuit. A fuse is thus a safety device which prevents damages to electrical circuits and possible fires. So we will not agree with an electrician, who is using a wire in place of fuse of proper rating as if by accident the current exceeds safe limit, the wires may become overheated and may cause fire.

1. Due to the low resistance and strength of aluminium and coppers, both these metals are usually employed for the transmission of electricity.
2. There is always an increase in the length of the wire with the increase in its resistance.
3. Since tungsten has high melting point and high resistance. So, that is why, the tungsten is used exclusively for filament of electric lamp.

The electrician cannot be allowed to replace the fuse in the house by a piece of wire. This is because every wire cannot be used as a fuse filament. A fuse filament must have a low melting point such that it could melt and break in response of large amount of current. Most of the wires have high melting points.

1. Used in cranes in steelworks and scrapyards.
2. Used to remove foreign bodies like iron filings from a patient’s body.
3. Used in electric bells, loudspeakers, etc.
4. Used in modern trams and trains.

One of the reasons may be that the rubber band used in the cell holder may not be tight enough to keep the two cells in contact with each other. If the cells are not in proper contact with each other, then the circuit will not be complete and current will not flow through the circuit. Hence, the bulb will not glow. The other reason may be that the two cells are not connected properly. The negative terminal of one cell must be connected to the positive terminal of the other cell.

The amount of heat produced in a wire depends on:

1. Its material: Better conductors produce less heat; e.g. Elements of electric appliances are made of nichrome whereas connecting wires are made up of copper which is a better conductor so they do not get heated up as the element.

2. Its length: As length increases heat produced increases; e.g. elements are coiled in heaters to increase length.

3. Thickness: As thickness increases heat produced decreases; e.g. lead wires of iron, heater etc. are thicker than normal connecting wire so that they don’t get heated up easily.

Earth wire is the insulated green coloured copper wire which is connected to a metal plate deep inside the earth near the house. It is used as a safety measure. It is kept at zero potential by connecting it to the ground, thus, providing a low-resistance conducting path for the current. When by electric fault, if current flows through the metallic body of electric appliance and we touch it, then current finds the lower resistance path of earth wire than our body. So, current flows through earth wire only and we remain safe.

When an electric current flows through a wire, the wire gets heated. It is the heating effect of current or When current flows through a metal wire it gets heated up, this is called heating effect of current. e.g. a glowing electric bulb becomes warm. This effect has many applications like Electric Heater, Light Bulb etc. When an electric current flows through a wire, it produces magnetic effect around it. A current carrying coil of an insulated wire wrapped around a piece of iron is called an electromagnet. Magnetic Effect of electric current has many applications like Electric Bell, Motor, Fan etc.

The factors which govern the force experienced by conductor which is placed in a uniform magnetic field are:

1. Strength of the magnetic field in which conductor is placed.
2. Strength of current flowing through the conductor.
3. Length of conductor.

When a current is switched on through a wire, the wire starts behaving as a magnet. Hence, when a compass needle is placed near the given current carrying wire, it gets influenced by the magnetic effect of electric current and gets deflected from its North- South position.

The bulb in the circuit is not glowing because the two cells are not connected properly. To make the bulb glow, the negative terminal of one cell should be connected to the positive terminal of the other cell, as shown in the given figure.

Short-circuiting occurs in a circuit when the live wire comes in direct contact with the neutral wire. This causes much damage to the electric appliances connected with them. Reason of short circuiting. When the live wire touches the neutral wire, the contact portion of the two wires behave like load and due to very low resistance of copper wire, it draws very large amount of current. In the presence of this high current, the copper wire catches fire, due to joules heating effect.

When live and neutral wire touches each other directly then it leads to short circuit in which the large amount of current flows through the household wiring and this large current may heat the wires to a dangerously high temperature and a fire may be started. Pulkit's father seems very sensible in taking the decisions and he showed a very great concern towards his son.

(i)	Electric cell
(ii)	Switch in off position.
(iii)	Electric bulb.
(iv)	Battery.