12.1

Question 1

When do we say there is electric current in a conductor?

Answer 1

Similarly, if the electric charge flows through a conductor (for example, through a metallic wire), we say that there is an electric current in the conductor.

Question 2

In a torch, what provides the charge that makes the torch glow?

Answer 2

In a torch, we know that the cells (or a battery, when placed in proper order) provide flow of charges or an electric current through the torch bulb to glow.

Question 3

What does a switch do?

Answer 3

A switch makes a conducting link between the cell and the bulb.

Question 4

Define electric circuit.

Answer 4

A continuous and closed path of an electric current is called an electric circuit.

Question 5

How do we express electric current?

Answer 5

Electric current is expressed by the amount of charge flowing through a particular area in unit time. It is basically the rate of flow of charges through a conductor.

Question 6

Direction of current.

Answer 6

Electric current was considered to be the flow of positive charges and the direction of flow of positive charges was taken to be the
direction of electric current. Conventionally, in an electric circuit the direction of electric current is taken as opposite to the direction of the flow of electrons, which are negative charges.

Question 7

Current definition.

Answer 7

If a net charge Q, flows across any cross section of a conductor in time t, then the current I, through the cross-section I=Q/t.

Question 8

Current formula.

Answer 8

I (current) = Q (charge) / t (time in seconds)

Question 9

Charge and its SI unit.

Answer 9

The SI unit of electric charge is coulomb (C), which is equivalent to the charge contained in nearly 6.25 × 10^18 electrons.

Question 10

Define charge.

Answer 10

It is a property of matter to attract or repel other materials. It is denoted by Q and its SI unit is Coulomb (C).

Question 11

Charge in electron and proton.

Answer 11

1.6 * 10^-19 C > -ve charge in electrons.
1.6 * 10^-19 C > +ve charge in protons.

Question 12

Define current.

Answer 12

Current is the amount of charge flowing through a particular area in unit time. It is the rate of flow of charges. If a charge Q flowed through a cross section in time t then current I would be = Q/t.

Question 13

Current SI unit.

Answer 13

The SI unit of current is Ampere.

1 Ampere = 1Coulomb/1 second
1 A = 1 C / 1 s

Question 14

Milliampere and Microampere.

Answer 14

milliampere = 1 mA = 10^–3 A
microampere = 1 μA = 10^–6 A

Question 15

What is an ammeter? What device measures current?

Answer 15

An instrument called ammeter measures electric current in a circuit. It is always connected in series in a circuit through which the current is to be measured.

Question 16

Schematic diagram of a circuit.

Answer 16

_____________M_______________
| |
| |
^ A
| |
|___|I|I|I _________<___(.)____|

M is bulb
|I|I|I is battery
(.) is a plug key
A is ammeter.

Question 17

what direction does current flow?

Answer 17

Note that the electric current flows in the circuit from the positive terminal of the cell to the negative terminal of the cell through the bulb and ammeter.

Question 18

A current of 0.5 A is drawn by a filament of an electric bulb for 10 minutes. Find the amount of electric charge that flows through the circuit.

Answer 18

We are given, I = 0.5 A; t = 10 min = 600 s.
From eq. we have
I= Q/t
so, Q = It
=> Q = 0.5 A × 600 s
=> Q = 300 C

Question 19

What does an electric circuit mean?

Answer 19

An electric circuit is a closed continuous path of electric current.

Question 20

Define the unit of current.

Answer 20

The SI unit of current is Ampere.
1 Ampere is the amount of current when 1 Coulomb of charge flows through a conductor in one second.

Question 21

Calculate the number of electrons constituting one coulomb of charge.

Answer 21

6.25 * 10^18 electrons constitute one coulomb of charge.