15 Electric Current And Its Effect
1. Choose the correct option.
(a) The strength of the magnetic field of a solenoid can be increased by (U)
(i) increasing the number of turns of the coil of the solenoid
(ii) decreasing the amount of current flowing through the solenoid.
(iii) decreasing the number of turns of the coil of the solenoid
(iv) replacing the iron core with ceramic
increasing the number of turns of the coil of the solenoid
(b) When the potential difference between the two points is zero, then (U)
(i) no electrical current will flow between these points
(ii) the electrical current will flow from positive terminal to negative
terminal
(iii) the electrical current will flow from negative terminal to positive
terminal
(iv) the electrical current will flow in any direction
no electrical current will flow between these points
(c) Which of the following is a symbol of the light bulb? (Ap)
(i) (ii)
(iii) (iv)
ans:
2. State whether the following statements are true or false. (U)
(a) An electric bell works on the principal of electromagnets.
True
(b) We should not touch electric components with wet hands.
True
(c) A battery converts electrical energy into chemical energy.
False
3. Name the following. (U)
(a) A device used to measure the amount of electric current flowing through a
circuit
Ammeter
(b) A cylindrical coil of an insulated metal wire.
Solenoid
(c) The path along which an electric current can flow.
Electric circuit
4. In the following questions, two statements are given- one labelled Assertion
(A) and the other labelled Reason (R). Read the statements carefully and
choose the correct alternative (A), (B), (C) and (D) as given below. (An)
(A) Both A and R are true and R is the correct explanation of the assertion.
(B) Both A and R are true but R is not the correct explanation of the assertion.
(C) A is true but R is false.
(D) A is false but R is true.
(a) Assertion: Conducting wires are made up of metals.
Reason : Metals are good conductors of electricity.
(A) Both A and R are true and R is the correct explanation of the
assertion.
(b) Assertion: A fuse is used as a safety device in a circuit against overloading of
current.
Reason : A fuse has a high melting point.
(D) A is true but R is false.
5. Explain the following. (R)
(a) Magnetic field
The region in the vicinity of a magnet, where the force of attraction or
repulsion can be felt by magnetic materials, is called a magnetic field.
(b) Lighting effect of electricity
When an electric current is passed through a conductor, it becomes hot
which in turn glows and produces light. This is called lighting effect of an
electric current.
6. State the function of the following: (R)
(a) Resistor
Resistor reduces the flow of electric current in electric circuits.
(b) Electric cell
Electric cell is used to apply a potential difference between the two ends
of a conductor.
7. Answer the following questions in detail.
(a) How are electromagnets useful? (Give three points) (R)
Electromagnets are used in various electrical appliances such as
electric bell, electric fan, electric motor etc.
Electromagnets are also used for the preparation of strong
permanent magnets.
Doctors use very small electromagnetic devices to take out small
magnetic materials from eyes, ears and nose.
Very strong electromagnets are used for magnetic separation of iron
ores.
Strong electromagnets are used in heavy industrial cranes to lift,
move and drop heavy iron and steel objects like cars.
(b) On which factors does the amount of heat produced by the flow of current
through a wire depend? (R)
The amount of heat produced by the flow of current through a wire
depends on the following factors:
Material of the wire
Thickness of the wire
Length of the wire
Amount of the current flowing through it
8. Make a flow chart to explain the working of an electrical bell. (Ap)
When the switch is pressed on, a current flows
through the electromagnet.
The electromagnet attracts the iron rod towards
itself, causing the hammer to strike the gong.
At the same time, the armature loses contact
with the screw and the current is switched off.
This causes the electromagnet to lose its
magnetism and the armature springs back to its
original position to close the circuit once again.
Current flows again and the cycle repeats itself
till the current is switched off.
9. Observe the circuit diagram and answer the questions that follow: (U)
fig A fig B
In which of the above circuits will the LED glow? Why?
fig B, because the switch in fig B is closed
10. A student connects a circuit as shown in the diagram. He switches on the circuit,
and places a sewing needle, a brass screw and a coin near the iron nail one by
one.
Which of the materials will be attracted towards iron nail? Why? (An)
The iron nail behaves like a magnet as long as current flows through the
circuit. The sewing needle and the coin are attracted towards the iron nail as
they are made of magnetic materials.
11. Who am I ? (U)
1. I drift forever with the current down the long canals they have made
I run elusive, multitasking to your aid
Before I came, the world was darker
But though I might make living easy, I am good at killing people too
Electricity
2. I automatically switch off an electrical circuit when the current in it exceeds
the specified maximum limit
You can lift me and switch me on with ease
I am better than a fuse.
MCB or Miniature Circuit Breaker
3. I have the N E W S on but I am not a TV
I will help you to find your way
I deflect in the presence of an electric current
Magnetic needle or compass
4. I am connected in an electric circuit. I will help to show you the potential
difference.
Voltmeter
I. HOTS questions
Ansh took a nichrome wire whereas Pranali took a copper wire of the same
length and thickness. Both of them connected the wires in a circuit. Will the
amount of current flowing in both circuits be the same? Explain.
(U)
No, the resistance of the nichrome wire is more than that of the copper
wire.
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