Question of Exercise 1

# Question The magnification produced by a concave mirror

Option 1 is always more than one

Option 2 is always less than one

Option 3 is always equal to one

Option 4 may be less than or greater than one

An electric motor works on the principle

A: of electromagnetic induction

B: when a rectangular coil is placed in a magnetic field and current is passed through it, a force acts on the coil which rotates it continuously.

C: both A and B

D: None of the above

Solution:

Explanation:

In an electric motor the electrical energy is converted into the mechanical energy.

And the motor used the magnetic effect of the current.

It is saying that when a rectangular coil is placed in a magnetic field and current is passing through it then a force is exerted in the coil which rotates the coil.

The option(B) is correct.

State joules law of heating

Solution:

Explanation:

It is used to calculate the rate at which electric energy is converting into the heat energy due to electrical resistance.

The formula of joule’s law of heating is Q = I2RT

Here, Q is the heat energy, I is the electric current, R is electric resistance and T is the time interval.

Hence, the  joule's law of heating is = I2RT.

Write Joules law of heating

Solution:

Explanation:

• A conductor becomes heated when an electric current flows through it for a long time. Joule's law of heating describes

the heating of a conductor caused by the flow of electric current across it.

Heat geretated

H=i2Rt

Here, i is the current running through the conductor, R is thHe conductor's resistance, and t is the length of time the current has flown.

Hence, Joule’s law of heating is given by H=i2Rt.

Name some devices in which electric motors are used

Solution:

Explanation:

• In contrast to an electric generator, an electric motor is a device that converts electricity into mechanical energy.
• They work on the basis of electromagnetism, which states that when an electric current is present in a magnetic field, a force is applied.
• Motors feature a lot of moving elements that allow them to spin and provide power as needed.

Electric motors that are used in certain devices are:

1. Pumps for water
2. Fans with electricity
3. Mixers with electricity
4. Machines for washing

Some devices in which electric motors are used are water pumps, electric fans, electric mixers, washing machines, etc.

What is symbol of battery

Solution:

Explanation:

A cell has two terminals: positive and negative.

The longer side represents the positive terminal and other is the negative terminal.

A battery is made up of more than two cells. Hence, the symbol of battery is: