Give reasons for the following questions:

Q1. Why never touch a lighted electric bulb connected to the mains?

Ans:

Never touch a lighted electric bulb connected to the mains because:

• It may be very hot & your hand may get burnt badly.
• You may get an electric shock, which may be dangerous.

Q2. There was a small fire in Rohan's house in the main electric circuit board. Can you state the reason why this may have happened? 

Ans:

This may have happened because of flow of excessive current through the electrical circuits due to the following reasons:

• The wires may have come in direct contact with each other causing short circuit.
• This may have happened due to damaged or faulty wiring or wear & tear of insulation of wires. 
• Another reason can be the connection of many devices to a single socket causing overloading.
• Thus short circuits & overloading can cause excessive current to pass through the circuit which can cause fire.

Q3. Why MCB's are being used instead of fuse?

Ans:

• MCB's or miniature circuit boards are switches that turn off automatically when current in a circuit exceeds the safe limit.
• They are a safety device & act like a fuse to protect the circuit from excessive flow of current.
• MCB's are easy to use as they can be turned on & the circuit is complete again.
• Whereas in the fuse, the wire melts & breaks. Hence after the issue is solved the fuse needs to be repaired.

Q4. Why not to keep the switch in the ‘ON’ position in a circuit with cells or battery for a long time?

Ans:

Not to keep the switch in the ‘ON’ position for a long time as the cells may become weak very quickly.

Q5. Why we use different wires for different requirements?

Ans:

We use different wires for different requirements because:

The amount of heat produced in a wire depends on its material, length & thickness of the wire.

Q6. How does an electric bulb glow?

Ans:

An electric bulb glows because:

• It consists of a wire of high melting point like tungsten called the filament.
• When electric current passes through the filament, it gets heated to a high temperature & it glows.

Q7. Why should we use symbols in circuit diagrams?

Ans:

We should use symbols in circuit diagrams because:

• It makes it easier to draw the diagrams with symbols.
• To draw components is hard & time consuming.
• Symbols make it easier to understand circuits.

Q8. Why are fuses important in electrical circuits?

Ans:

• A fuse is a safety device which prevents excessive current from flowing in the electrical circuit.
• The fuse wire melts as it has low melting point.
• Hence the wire breaks immediately when excessive current passes through the circuit.
• This prevents fires and damage to appliances or circuit.

Q9. Why a copper wire is not used for making electric fuse?

Ans:

• A fuse requires a wire with low melting point so that it can break the circuit when excessive current is flowing through it.
• A copper wire has high melting point and very low resistance.
• Hence when excessive current is flowing through the circuit, the copper wire will not melt and allow the current to flow without breaking the circuit.
• The copper wire will not protect the electrical appliances from excessive current.

Q10. Why LED's are preferable over incandescent electric bulbs?

Ans:

• Incandescent electric bulbs are often used for lighting but they also give heat.
• It means that a part of electricity is consumed in producing this heat.
• This leads to wastage of electricity.
• LED bulbs consume less electricity as compared to incandescent bulbs.
• As LED bulbs are electricity efficient, they are preferred over incandescent electric bulbs.

Answer the following questions in short:

Q1. What is the function of a cell holder?

Ans:

The cell holder maintains a stable connection between the battery terminals & the circuit, ensuring continuous power supply.

Q2. What is an electromagnet?

Ans:

• It is a coil of wire wrapped around iron.
• When current flows through it, it acts like a magnet.

Q3. What happens to a compass needle near a current-carrying wire?

Ans:

When electric current flows through a wire it acts like a magnet deflecting the compass needle.

Q4. What is the effect of electric current in a room heater?

Ans:

The coil or element of the electric heater get heated when electric current passes through it due to heating effect of current making the room warm.

Q5. How do you connect cells to make a battery?

Ans:

• Connect the positive terminal of one cell to the negative of the next.
• Or use a cell holder for better stable connections.

Q7. What is the role of a switch in an electric circuit?

Ans:

A switch can open (does not allow current to flow) or close (completes the circuit allowing the current to flow) the circuit, thus controlling the flow of electric current in the circuit.

Q8. What is the difference between a battery and a cell?

Ans:

• A cell is a single unit that produces electricity.
• A battery is a combination of two or more cells.

Q9. In which devices heating effect of electric current is used?

Ans:

The devices in which heating effect of electric current is used are: electric bulb, room heater, immersion heaters, hotplates, irons, geysers, electric kettles, hair dryers, etc.

Q10. Give uses of electromagnet.

Ans:

Uses of electromagnet are: electric bells, by doctors to remove magnetic material accidentally fallen in eye, toys & to lift heavy magnetic loads.

Answer the following questions:

Q1. What is a short circuit? What are the causes of a short circuit?

Ans:

1. Short Circuit: A sudden flow of a very large current due to direct contact of a live and neutral wire is called a short circuit. 
2. Causes: Sometimes the live wire and neutral wire in a circuit touch each other due to defective and damaged wiring. Because of this, the resistance of the circuit becomes almost zero & very large current flows through it.

Q2. What is overloading?

Ans:

1.  When too many electrical appliances are connected to a single socket, they draw an extremely large current flow from the household circuit.
2. The household wiring gets overheated. The overheating of electrical wire in any circuit due to the flow of a large current through it is called overloading.

Q3. Write the working and applications of the heating effect of electric current.

Ans:

1. All electric heating appliances contain a coil of high resistance wire like nichrome called the element.
2. When electric current is passed through the element, it becomes red hot & gives out heat. This heat is then put to desired use by the electric appliance.
3. Applications: Electric heating appliances such as electric iron, electric toaster, electric oven, electric heater, geyser, etc. work on this heating effect.

Q4. What is an electric fuse? Explain its working.

Ans:

Fuse:

It is a safety device which melts & breaks the circuit when there is excessive flow of electric current preventing damage to the electrical appliance & possible electric fire.

Principle: It works on heating effect of electric current.

Working of a fuse:

1.  A fuse consists of a piece thin wire having a low melting point.
2. When there is flow of excessive current fuse wire gets heated & melts which breaks the circuit immediately.
3. The current flow in the circuit stops preventing damage to the electrical appliances.

Q5. Explain the working of an electric bell.

Ans:

1. It works on the principle of magnetic effect of electric current.
2. It converts electrical energy to sound energy.
3. It consists of a coil of wire wound on an iron piece which acts like a electromagnet.
4. There is iron strip with a hammer at one end which is close to the electromagnet.
5. The other end of this strip is near a contact screw.
6. When the iron strip is in contact with the screw, the current flows through the coil which acts like a electromagnet & pulls the iron strip.
7. Due to this pull the hammer at the end of the strip strikes the gong to produce the sound.
8. The pull also breaks the circuit & the current stops flowing through the circuit.

Q6. State the differences between open & closed circuit.

Ans:

Open circuit	Closed circuit
Switch is in 'OFF' position.	Switch is in 'ON' position.
Circuit is incomplete.	Circuit is complete.
Electric current dow not flow.	Electric current flows.
Bulb does not glow.	Bulb glows.