Magnetic effect of electric current
V.S.A.Q (1 marks)
1. What constitute the field of a magnet?
Ans. The space around a magnet within which its magnetic effect can be experienced, constitutes the (magnetic) field of the magnet.
What is meant by the following? A fuse is rated at 8 A?
Ans. It means that it burn if current exceeds 8A.
What is short circuiting in an electric supply?
Ans. Short circuiting in an electric supply occurs when the live wire touches the neutral wire.
What happens when a current carrying conductor is kept in a magnetic field?
Ans. It experience a force.
Are magnetic field lines open or closed curves?
Ans. They are closed curves.
6. What is the frequency of AC in India?
Ans. It is 50 Hz.
SAQ (2 marks)
1. Write down any two properties of magnetic field lines.
Ans. 1 It is directed from north pole to south-pole outside the magnet and inside the magnet it is vice-versa.
2.Two magnetic field lines never intersect each other.
2. What is electro-magnetic induction?
Ans. In reality it is the conversion of mechanical energy into electrical energy.
3.What is the role of each of the three pins in a power plug?
Ans. The thick pin at the top of a power plug is for earthing ,the live pin is on the left and the neutral pin is on the right of the power plug.
what are the two main precautions to be the taken while using an electric supply?
Ans. (i)Electric supply should be immediately switched off from the main switch in case a person touches a live wire or if there is a fire in the house.
(ii) Electric supply should also be switched off during natural calamities like earthquake, floods etc.
What is the difference between two circuits used in household electricity?
Ans. One of 15 ampere rating is used for higher power appliances and second of 5 ampere rating is used for bulbs, fans, etc. which are of lower power rating.
Two wires A and B suspended. These wires are connected in parallel with a battery as shown in figure. Will the distance of separation between the wires (i) remains the same or (ii) increases or (iii) decreases? Explain.
Ans. When wires are connected to battery in parallel, then the current in both the wires will attract each other, therefore the distance between the wire decreases.
SAQ (3 marks)
1. A circuit has a fuser of 5 A. What is the maximum number of 100 watt (220v) bulbs this can be safely used in the circuit?
Ans. Suppose x number of such bulbs can be used.
Power of one bulb =100 watt
Power of x bulb (p)=100 x X watts
Potential difference(v)=220 volts.
= 100 x X= 220×5
X =220×5/100=11 bulbs
2. On what factors does the force experienced by a current carrying conductor placed in a uniform magnetic field depend?
Ans. The place in a uniform magnetic field depends on :-
(i) The length of the conductors(l).
(ii) The magnitude of current flowing through the conductor (l), and
(iii) The magnitude of the magnetic field of the conductor (B)
3. A fixed wire AB carries current I. An electron is moving parallel to the wire in which direction does the electron tend to move?
Ans. By right hand thumb rule, the magnetic field in the vicinity of wire is downward, perpendicular to the plane of the paper. The conventional direction of electrical current his opposite to the direction of motion of electron. By Fleming left hand rule the force on electron is always away from wire in the plane of paper; therefore, the electron will be deflected downward (away from the wire) in the plane of paper.
4. A cylindrical bar magnet is kept along the axis of a circular coil. Will there be a current induced in the coil if the magnet is rotated about the axis?
Ans. The magnetic field of a cylindrical magnet his symmetrical about the axis. As the magnet is placed along the axis of circular coil, there will be no induced current because the magnetic flux linked with the coil does not change due to rotation of the magnet.
LAQ (5 marks)
Answer the following
i. What is the phenomenon of electron magnetic induction?
ii. Which is the device used for producing current?
iii. What is the essential difference between AC generator and a DC generator?
iv. At the time short circuit, what happens to the current in the circuit?
v. Give the role of split ring in AC generator?
Ans. i) the phenomenon of electromagnetic induction is producing induced current in a coil due to relative motion between a magnet and the coil.
ii) The device used for producing current is generator
iii) The essential difference between an AC generator and DC generator is that AC generator has slip rings while the DC generator has a commutator.
iv) At the time of short circuit, the current in the circuit increases heavily.
v) The role of split ring is to reverse the direction of current through a circuit.