Explore topic-wise InterviewSolutions in .

i) • Disha connected wire A with both the batteries. 

• When wire A was connected with 3v battery, Disha found that the wire started heating. 

• When the wire A was connected with 12V battery, she found that the wire is emitting a large amount of heat. 

• Thus, she concluded that wire A is a nichrome wire as nichrome wire has a very large resistance and it produces a large amount of heat. 

ii) • Disha connected wire B with both the batteries. 

• When wire B was connected with 3v battery, did not find anything. 

• When the wire B was connected with 12V battery, she found that the wire has started melting and. 

• Thus, she concluded that wire B is a fuse wire as fuse wire has a very low melting point and it melts as a large amount of current is made to pass through it.

P=920W, V=230V, I=? 

We know that 

P = V x I, 

920 = 230 x I

I = 920/230 = 4amp

Though silver is a very good conductor of electricity but still that is not used in electric wiring primarily due to its cost. It's very expensive compared to the widely used wiring material copper. Another reason for not using silver is that , it oxidizes easily and tarnishes when it comes in contact with air.

Solution :

The potential difference between two points is 1 volt means 1 joule of work is done in moving 1 coulomb of electric charge from one point to the other.

Solution : 

(a) If three cells of 2 volt each are connected in series to make a battery, then the total potential difference between terminals of the battery will be 6V. 

(b) (i) Given: p.d. = 2V, Charge moved = 1C 

We know that 

Work done = p.d. x charge moved = 2 x 1 

Work done = 2 joules 

(ii) Given: p.d. = 6V, 

Charge moved = 1C 

Work done = p.d. x charge moved = 6 x1 

Work done = 6 joule. 

Solution : 

Voltmeter has a high resistance so that it takes a negligible current from the circuit.

Since the voltmeter reading shows 2V. Thus V = 2.

Also, Current send by electric cell = 0.4A 

Thus I = 0.4A 

By Ohm’s law V = IR 

⇒ 2 = 0.4 × R 

⇒ R = \(\frac{2}{0.4}=\frac{20}{4}\) = 5Ω

The resistance of the resistor is 5Ω.

Solution : 

The electrical property of a material is known as Resistance

The ammeter must be connected in the series to read the current correctly. Ammeter has very low resistance If it is connected in parallel across any load then all current in circuit will choose lower resistive path (i.e ammeter) which will cause the circuit to be damaged. Hence it is used in series. Also the current in the series is always same

Given 

Resistance (R) = 2Ω 

Area of cross-section = A 

Length = l 

We know that R = \(ρ\frac{1}A\)

⇒ 2 = \(ρ\frac{1}A\) 

New Area = A/2 

New Length = 2l 

New Resistance = R’

⇒ R' = \(ρ\frac{2l}{\frac{A}{2}}\)

⇒ R' = \(ρ\frac{4l}{A}\)

 ⇒ R' = \(4ρ\frac{l}{A}\)

⇒ R' = 4 x 2 = 8, from (1)

Hence the new resistance will be four times the previous resistance i.e. 8Ω.

Because of the existence of resistance to the flow of current work has to be done in order to maintain the flow of current.

Since the potential difference V is the work done to carry unit positive charge from infinity to a point, the work done to carry a charge q is given by:

W= qV

But I = q/t

So W = ItV

Since V = I R

W = I²Rt = V²t/R

This work done is stored as energy.

SI unit of electrical energy is Joule.

Power rating of electric iron = 1 kW = 1000 W

V=220 V

P=VI

I=P/V=1000/220

=4.55 A

Hence, a fuse of rating 5A can be used because it can bear the current.

Miniature Circuit Breaker.

∴ R α l/a

More the area, lesser is the resistance and more is the current flowing.

∴ 15 A fuse wire is thick

Due to voltage fluctuations or insulation on the wire of cable gets worn and tom (breaks), the live wire comes in contact with the neutral wire and results in SHORT CIRCUIT. To prevent this damage, a fuse is used in the LIVE WIRE. The fuse wire gets heated up to the extent that it melts, a gap is produced in the live wire and the circuit becomes incomplete, no current flows and the appliance is saved.

The fuse breaks the circuit if a fault in an appliance causes too much current flow. This protects the wiring and the appliance if something goes wrong. The fuse contains a piece of wire that melts easily. If the current going through the fuse is too great, the wire heats up until it melts and breaks the circuit.

Copper wire cannot be used as a fuse wire since the melting point of Cu is higher and resistance is very low and current can flow through it without melting it and without breaking the circuit.

MATERIAL used is an ALLOY of LEAD (50%) and TIN 50% having low M.P. of 200°C

Two CHARACTERISTICS OF FUSE WIRE are:

(i) Has LOW MELTING POINT.

(ii) Has HIGH RESISTANCE.

FUSE: “Is a safety device which is used to limit the current in an electric circuit.

PURPOSE OF FUSE IN HOUSEHOLD CIRCUIT: It safeguards the circuit and the appliances connected in the circuit from being damaged if the current in the circuit exceeds the specified value due to voltage fluctuation or short-circuiting.

False 

A conducting wire offers resistance to the flow of electrons due to the random collision between the electrons and the stationery atoms.

Series : If the second terminal of the first device is connected to the first end of the second device such type of connection is called series connection.

Fluorescent tube : Fluorescent tube light is a light source, which is commonly known as tube light.

1. Electric cell, 

2. Iron nails – 2, 

3. Wooden board, 

4. Connecting wires, 

5. 10 cm of Nichrome wire etc.

Parallel : If all the first terminals of all the devices are connected to one point and all the second terminals are connected to another point such type of connection is called parallel connection.

Heating effect : The production of heat due to the flow of electricity through a wire is called heating effect of electricity.

Electric shock : An electric shock occurs when a person comes into contact with an electrical source and electricity flows through his body.

Magnetic effect : The production of magnetic force due to the flow of electricity through a wire is called magnetic effect of electricity

Fuse : The safety device which is used in electrical appliances to protect from damages when excess of electricity flows through them is called a electric fuse.

CFL : Compact Fluorescent Lamp is a light source.

MCB : Miniature Circuit Breaker is Na type of fuse which automatically turns off when electricity in a circuit exceeds the safe limit.