Explore topic-wise InterviewSolutions in .

Philospher Thales discovered it but it was satisfactorily explained by Dr Gilbert.

(i) Glass.

(ii) Ebonite.

(i) Negative charge.

(ii) Positive charge.

Aim— To show that there are two kinds of charges. 

Apparatus— gold leaf electroscope, glass rod rubbed with silk cloth. any two non-identical bodies say A and B. 

Procedure— 

(i) Charge the gold leaf electroscope positively by touching it with glass rod rubbed with a silk cloth. 

(ii) The gold leaf electroscope shows its charging by showing its leaves diverging. 

(iii) Touch the brass cap of this electroscope with body A-Note the divergence of the gold leaves. 

(iv) Now touch the brass cap with body Band note the divergence. 

Observation— In case of body A—Leaves further diverge. 

In case of body B — leaves converge. 

Inference— Body A (positively charged) Body B (negatively charged) 

So there are two types of charges.

A glass rod rubbed with silk i.e. +vely charged is brought near ebonite rod rubbed with fur i.e. negatively charged ATTRACTION is seen f as they have opposite charge.

High resistance of filament wire accounts for this difference

The filament wire becomes white hot where as other wires in the circuit do not get heated much. 

Solution : 

In first case, I = 0.02 amp, 

V = 10 volt 

V=IR 

10 = 0.02 x R 

R = 10/0.02 = 500 ohm 

In second case, 

I = 250 x 10-3 amp, 

R = 500 ohm V = IR 

V = 250 x 10-3 x 500 

V = 125 volt.

THREE SAFETY MEASURES DURING THUNDERSTORM: 

(i) Do not lie on the ground, but squat low on the ground with your hands on your knees and head in between. 

(ii) Take out the plugs of the T.V. sets, computers, etc. Do not use the wired phone. 

(iii) Do not take bath during the thunderstorms and avoid contact with running water or metallic tap. 

(iv) Do not carry an umbrella over your head particularly if walking in an open ground. If there are tree around, take shelter under a shorter tree.

Correct option  (c) 600 kw h 

Explanation:

 V= 260 V, P=2 k\N =2000 W

Time for which air conditioner is switched on is

t = 10 hours x 30 = 300 hours

Electrical energy consumed in 30 days

= P x t = 2000 x 300

= 600000 W h = 600 kW h

Electricity originated from the Greek words “Electrica” and “Elektron”.

The Greek Philosopher Thales was the first to observe the attracting capacity of certain materials when rubbed on other materials.

Gilbert classified these materials as Vitreous and Resinous.

These names were later changed to positive and negative charges.

Fur, Flannel, Wax, Glass, Cotton, Paper, Silk, Human skin, Wood, Metals, Rubber, Resin, Amber, Sulphur, Ebonite.

If any two materials in this series are rubbed against each other the element occurring first in series will acquire positive charge and the element occurring later will acquire negative charge.

When the temperature of the heater becomes greater than the temperature of the surrounding, some of the heat is lost to the surroundings in the form of thermal radiations. After some time, the rate at which heat is being produced becomes equal to the rate of which heat is lost. Hence, the temperature of the element becomes constant.

Ammeter ,A₂ shows a higher reading. Since wire ,A₁ is longer, it has greater resistance and so draws lesser current. So more current flows through B and ,A₂ shows a higher reading.

(i) Copper wire can be used for electrical transmission lines because copper has very low resistivity and hence it is a very good conductor of electricity.
(ii) Manganin can be used for electrical heating devices because the resistivity of manganin is about 25 times more than that of copper and hence it produces a lot of heat on a passage of current through it.

One Volt is the potential difference between two points in a current carrying conductor when 1 joule of work is done to move a charge of 1 coulomb from one point to the other.

Therefore 1Volt = \(\frac{1\,joule}{1\,columb}\)

1 V = 1 Jc^-1

The three resistance of 20 ohm, and 10 ohm and 20 ohm on the extreme right side are in series.

So, the resultant of these three resistances = 20+20+10 = 50 ohms

This 50 ohms is in parallel with 30 ohms. So resultant of these two will be 

1/R = 1/30 +1/50

1/R = 80/1500

R = 18.75 ohms

Now, the resistances 10 ohms, 18.75 ohms and 10 ohms are in series.

Therefore, resultat resistance = 18.75 + 10+ 10 = 38.75 ohms.

When the live wire comes in contact with the metal body of the electrical gadget.

Solution : 

(a) Resistance of a conductor increases (or decreases) with increase (or decrease) in the length of the conductor. 

(b) Resistance of a conductor decreases (increases) with increase (decrease) in the area of cross-section of the conductor. 

(c) Resistance of a conductor increases on raising the temperature and decreases on lowering the temperature. 

When we switched ON the bulb, electricity flows through the wire and makes the bulb glow.

A group of cells is called a battery.

Cell converts the chemical energy into electrical energy.

An  cell is a device, which converts chemical energy into electrical energy. It has two terminals, which are made up of metal: one terminal is positive, while the other one is negative. When the two terminals are connected to an electrical device, electric current flows through it.

• An electrochemical cell consists of electrodes namely cathode and anode.
• The non-spontaneous reaction is controlled by an external source of current.
• The decomposition of an electrolytic solution by passing current, which results in the liberation of corresponding gases or metals is known as electrolysis.

A cell is a device used to generate electricity.

The positive electrode is called anode.

The negative electrode is called cathode.

Cell mainly consists of two components, electrolyte, and electrodes.

Electrodes are two types :

positive and negative.

1) Dry cell, 

2) Lithium cell, 

3) Button ceils, 

4)Alkaline cell

1. Anode and cathode are the two electrodes in a cell. 

2. The positive electrode is called anode and the negative electrode is called cathode.

Electrolyte is a chemical component that conduct the electricity.

The electrolyte is a chemical component that conducts the electricity.

(d) should be able to form positive and negative ions

Electroplating.

(a) conductors

(c) insulator

1. d 

2. c 

3. a 

4. b

1. We know about symbols. We do indicate to our teacher that we wish to go out to drink water. 

2. We know the signs for addition, subtraction, multiplication and division. 

3. We might have used the symbols for ‘greater than’, ‘less than’, ‘equal to’ etc. 

4. Symbols play an important role in our life. 

5. They convey precise meaning with few descriptions. 

6. Some common electric components can be represented by standard symbols.

Correct option is A) Battery, fuse

Correct option is C) Miniature Circuit Breaker

The answer is (c) the shape of the resistor is changed

(a) A magnet has two poles. 

(b) Like poles repel each other and unlike poles attract. 

(c) An electromagnet is used to separate large mass of iron scrap. 

(d) The strength of magnetic field of an electromagnet is increased by inserting a core of soft iron. 

(e) In a torch we use dry cell as the source of electricity. 

(f) To light a table lamp and to run a refrigerator, we use mains as the source of electricity. 

(g) A group of two or more cells is called a battery. 

(h) Conductors pass electricity through them. 

(i) Insulators do not pass electricity through them.

(a) Silver is a better conductor due to its lower resistivity.
(b) Nichrome should be used in electrical heating devices due to very high resistivity.

Solution : 

(a) Good conductor = C (10 x 10-8ohm-m) 

(b) Resistor = A (110 x 10-8 ohm-m) 

(c) Insulator= B (1 x 1010 ohm-m) 

(d) Semiconductor= D (2.3 x 103 ohm-m)