# Question 1

What are conductors of electricity?

Solution:
Materials which allow electric current to pass through them are conductors of electricity.

# Question 2

Name some materials that are good conductors of electricity.

Solution:
Materials such as water, aluminium, copper, gold, etc. conduct electricity.

# Question 3

What are insulators?

Solution:

Materials, which do not allow electric current to pass through them easily, are insulators.

# Question 4

Give some examples of insulators.

Solution:
Materials such as rubber, plastic, wood do not conduct electricity.

# Question 5

In previous class you have used a tester as shown is figure given below to test whether electric current passed through a particular material or not? When this tester is used for liquids sometimes even though the liquid allows the electric current to pass and the circuit is complete, bulb does not glow. What can be the reason?
Solution:
Due to the heating effect of current, the filament of the bulb gets heated to such a high temperature that it starts glowing. However, if the current through a circuit is too small, the filament of the bulb does not get heated to a high temperature and it does not glow. The reason why is the current in the circuit small is that though a material may conduct electricity, it may not conduct it as easily as a metal. As a result, though the circuit of the tester becomes complete and the current flows through it, the current is too small.

# Question 6

What is LED? Why it can be used in place of a bulb in the tester?

Solution:
We may use a LED in place of electric bulb. LED glows even when a small electric current flows through it. There are two wires (called leads) attached to LED. One lead is slightly longer than the other one. Remember that while connecting a circuit the longer lead of LED is always connected to the positive of the battery and the shorter lead is connected to the negative terminal of battery.

# Question 7

How the magnetic effect of current can be used to detect current?

Solution:
When current flows in a wire, a compass needle kept nearby gets deflected. Even if the current is small, the deflection of the magnetic needle can be seen. We can use the magnetic effect of current to make another tester. For this, take a cardboard tray from inside a discarded matchbox. Wrap an electric wire a few times around the cardboard tray. Place a small compass needle inside it. Now connect one free end of the wire to a terminal of a two cell battery. From the other terminal of the battery, connect another wire. Your tester with two free ends of wire is ready (Fig. 14.7.)

# Question 8

Using the tester made is Q. 7 test the conductivity of liquids such as tap water, vegetable oil, milk, kerosene etc. and complete table:

 S. No Material Compass needle shows deflection Yes/No Conductor/Insulator 1. Lemon Juice Yes Conductor 2. Vinegar 3. Tap water 4. Vegetable oil 5. Milk 6. Honey

Solution:
 S. No Material Compass needle shows deflection Yes/No Conductor/Insulator 1. Lemon Juice Yes Conductor 2. Vinegar Yes Conductor 3. Tap water Yes Conductor 4. Vegetable oil No Insulator 5. Milk No Insulator 6. Honey No Insulator

# Question 9

What effect does the current produce when it flows through a conducting solution?

Solution:
The passage of an electric current through a conducting solution causes chemical reactions. As a result, bubbles of gas are formed, deposits of metal on electrodes may be seen and changes of colour of solution may occur, depending on what solutions and electrodes are used. These are some of the chemical effects of the electric current.

# Question 10

What is the application of chemical effects of electricity in our daily life? Give examples.

Solution:
Carrying chemical reactions by the effect of electricity is called chemical effect of electric current.

Example of Chemical Effect

Electroplating: One metal is coated on the other substance or metal by the effect of electric current. This is called electroplating.

Electrolysis: The compound is decomposed into its constituents under the effect of electric current is called electrolysis.

# Question 11

What is Electroplating?

Solution:
The process is depositing a layer of any desired metal on another metallic object by means of electricity is called electroplating. It is one of the common applications of chemical effects of electric current.

# Question 12

During electroplating the copper deposited on the plate connected to negative terminal comes from the solution. How this loss of copper from solution compensated?

Solution:
From the other plate an equal amount of copper gets dissolved in the solution. Thus the loss of copper from the solution gets compensated and the process keeps going. This means that copper gets transferred from one plate to another.

# Question 13

Give one example of the application of electroplating.

Solution:
Chromium plating is done on many objects such as car parts, bath taps, kitchen gas burners, bicycle handlebars and wheel rims.

# Question 14

Why chromium is used for electroplating? Why the objects which have chromium plating are not made of chromium itself?

Solution:
Chromium has a shiny appearance, does not corrode and resists scratches. However chromium is expensive and it may not be to make the whole object out of chromium. So the object is made from a cheaper metal and only a coating of chromium over it is done.

# Question 15

Except chromium plating on several other metals what other metals are used for waiting . Give few examples.

Solution:
Jewellery makers electroplate silver and gold on less expensive metals. These ornaments have the appearance of silver or gold but are much less expensive. Tin cans, used for storing food items, are made by electroplating a layer of tin onto iron. The tin is less reactive as compared to iron. Thus the food is protected, against spoilage, from the underlying iron by tin layer. Iron is used in bridges and automobiles to provide strength. However, iron tends to corrode and rust, so zinc is plated on to iron protect it from corrosion and the formation of rust.

# Question 16

Make a list of materials around you which conduct electricity and a list of those that do not.

Solution:
Conductors: Things formed of metals, e.g., copper, iron and aluminum, wet things and solutions of electrolytes in water.

Insulators: Dry things made of wood, rubber and plastics.