# Chapter – 4 -ELECTRIC CHARGE AND ELECTRIC CURRENT.

18 Nov 2020 7:37 am

Electric Charge and Electric Current, 9th std, science, tamilnadu, board,

## Question 1.

In current electricity, a positive charge refers to,………………

(a) presence of electron

(b) presence of proton

(c) absence of electron

(d) absence of proton

(c) absence of electron

## Question 2.

Rubbing of comb with hair ……………………

(a) creates electric charge

(b) transfers electric charge

(c) either (a) or (b)

(d) neither (a) nor (b)

(c) either (a) or (b)

## Question 3.

Electric field lines ………….. from positive charge and ………. in negative charge.

(a) start; start

(b) start; end

(c) start: end

(d) end; end

(b) start; end

## Question 4.

Potential near a charge is the measure of its ………… to bring a positive charge at that point.

(a) force

(b) ability

(c) tendency

(d) work

(d) work

## Question 5.

In an electrolyte the current is due to the flow of …………. .

(a) electrons

(b) positive ions

(c) both (a) and (b)

(d) neither (a) nor (b)

(a) electrons

## Question 6.

Heating effect of current is called

(a) Joule heating

(b) Coulomb heating

(c) Voltage heating

(d) Ampere heating

(a) Joule heating

## Question 7.

Electroplating is an example for

(a) heating effect

(b) chemical effect

(c) flowing effect

(d) magnetic effect

(b) chemical effect

## Question 8.

Resistance of a wire depends on

(a) temperature

(b) geometry

(c) nature of material

(d) all the above

all the above

1. (c)
2. (e)
3. (d)
4. (a)
5. (b)

## Question 1.

Electrically neutral means it is either zero or equal positive and negative charges

True

## Question 2.

Ammeter is connected in parallel in any electric circuit

False

Correct Statement: An ammeter is connected in series with a device to measure its current.

## Question 3.

The anode in electrolyte is negative

False

Correct Statement: The anode in electrolyte is positive.

## Question 4.

Current can produce magnetic field

True

## IV. Fill in the blanks.

1. Electrons move from ………….. potential to …………….. potential.
2. The direction opposite to the movement of electron is called ……………….. current.
3. The e.m.f of a cell is analogous to ……………. of a pipe line.
4. The domestic electricity in India is an ac with a frequency of ………… Hz.
5. Trip switch is an …………. safety device

1. higher, lower
2. Conventional
3. a pump
4. 50
5. electromechanical

## Question 1.

A bird sitting on a high power electric line is still safe. How?

Birds don’t get shocked when they sit on electrical wires because they are not good conductors of electricity.

Electricity flowing through a single power line at 35,000 volts will continue along the path of least resistance and bypass birds, because there is no difference in electrical potential.

## Question 2.

Does a solar cell always maintain the potential across its terminals constant? Discuss.

The electro-chemical process inside a battery provides electrons at the negative terminal and draws electrons from the positive terminal to maintain the current being drawn.

By providing energy to the electrons, the cell is capable of maintaining an electric potential difference across the two ends of the external circuit.

## Question 3.

Can electroplating be possible with alternating current?

Electroplating is a process where there is continuous flow of ions for the deposistion of copper, which is not possible in Alternating current.

Therefore, electroplating is possible with DC only, for the sake of perfectness and homogeneity of the electroplating.

## Question 1.

On what factors does the electrostatic force between two charges depend?

The electrostatic force between two charges depend on the following factors;

1. value of charges on them,
2. distance between them, and
3. nature of medium between them.

## Question 2.

What are electric lines of force?

The direction of the electric field is the direction of the force that would act on a small positive charge.

Therefore the lines representing the electric field are called ‘electric lines of force’.

## Question 3.

Define electric field.

The electric lines of force are straight or curved paths along which a unit positive charge tends to move in the electric field.

Question 4.

Define electric current and give its unit.

Current is the rate at which charges flow past a point on a circuit.

Current (I) is represented as, I =

q

t

The standard SI unit for current is ampere with the symbol A.

Question 5.

State Ohm’s law.

Ohm’s law states that electric potential difference across two points in an electrical circuit is directly proportional to the current passing through it. That is,

V~I

The proportionality constant is tne resistance (R) offered between the two points.

Hence, Ohm’s law is written as,

V = RI (or) V = IR

Where, V is the potential difference in volt (V), I is the current flow in ampere (A), R is the resistance in ohm (Ω)

Question 6.

Name any two appliances which work under the principle of heating effect of current.

The principle of all electric heating appliances like iron box, water heater, toaster etc.

work under the principle of heating effect of current.

Question 7.

How are the home appliances connected in general, in series or parallel. Give reasons.

The home appliances are connected in parallel.

This is because, when the appliances are connected in parallel, each of them can be switched on and off independently.

This is a feature that is essential in a house wiring.

Also, if the appliances were wired in series, the potential difference across each appliance would vary depending on the resistance of the appliance.

Question 8.

List the safety features while handling with electricity.

Safety features to be followed are:

1. Ground connection
2. Trip switch
3. Fuse.

## VII. Exercises.

Question 1.

Rubbing a comb on hair makes the comb get – 0.4C.

(a) Find which material has lost electron and which one gained it.

The material is comb which gained electrons and the hair gained it.

(b) Find how many electrons are transferred in this process.

Charge on 1 electron,

e = 1.6 × 10– 19C

q = ne or n =

q

e

n =

0.4

1.6

× 10– 19 = 0.25 × 1019 = 2.5 × 1018

Question 2.

Calculate the amount of charge that would flow in 2 hours through an element of an electric bulb drawing a current of 2.5A.

Given: Time ‘t’ = 2 hours = 2 × 60 × 60s

t = 7200s

I = 2.5A

Amount of charge, Q = I × t

= 2.5 × 7200

Q = 18000C

Question 3.

The values of current I flowing through a resistor for various potential differences V across the resistor are given below. What is the value of resistor?

[Hint: plot V-I a graph and take slope].

Resistance(R) = $$\frac { ∆V }{ ∆I }$$

= 10.2 –

6.7

3

– 2 = 3.5/1

R = 3.5Ω

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