Plus Two Physics Chapter Wise Previous Questions Chapter 6 Electromagnetic Induction is part of Kerala Plus Two Physics Chapter Wise Previous Questions and Answers Kerala. Here we have given Plus Two Physics Chapter Wise Questions and Answers Chapter 6 Electromagnetic Induction.
Kerala Plus Two Physics Chapter Wise Previous Questions Chapter 6 Electromagnetic Induction
Question 1.
An Aluminium ring is placed around the projecting core of a powerful electromagnet as shown in the figure below. When the circuit is closed the ring jumps up to a surprising height. Why? (March – 2009)
Answer:
The closing of circuit increase magnetic flux through the ring which induces a current in it. According to Lenz’s Law, current in the ring circulates to oppose the current in the windings of coil. This current is called eddy current. The two oppositely behaving dipoles repel each other, sending the ring upward.
Question 2.
Self-inductance of a coil plays the role of inertia in a circuit. (March – 2010)
a) The SI unit of self-inductance is
b) Current in a circuit falls from 5A to 1A in 0.1. second. If an average EMF of 200 volts is induced, find the self-inductance of the coil.
Answer:
a) Henry
Question 3.
Sometimes when we switch off the electrical equipment, a spark is seen within the switch. This is explained on the basis of electromagnetic induction. (March – 2011)
a) What is self-induction?
b) Current in a circuit falls from 5A to 0A in 0.1 S. If an average emf of 200v is induced, determine the self-inductance the circuit.
Answer:
a) A current through a coil produces a magnetic field in it. When the current flowing through the coil changes the magnetic flux associated with the coil changes. This change in flux induces an emf in the coil. This emf is called self-induced e.m.f. or back e.m.f. This phenomenon of production of back emf in coil is called self-induction.
Question 4.
A steady current of 1 amperes is passed through a long solenoid of length 1 and number of turns N. (Say – 2011)
a) Obtain a relation for the self-inductance of the solenoid.
b) The self-inductance of a coil is 2 mH. If a current of 1A is switched off in a time of one millisecond, what is the induced emf in it?
c) When an alternating current is applied to an electrical element, the current in it leads the voltage by π/2. Identify the element.
Answer:
a) Consider a coil of N turns having area A. Let I be the current flowing through the coil. Let n be the number of turns per unit length and / be the length of coil.
If ϕ is the flux linked with single turn,
Total flux = Nϕ
This total flux is directly proportional to the current passing through it.
ie. Nϕ > α l
Nϕ = LI ………………… (1)
where L is called the coefficient of self-induction or self-inductance.
We can also write Nϕ = N B A
Comparing eq(1) and eq(2)
c) Capacitor
Question 5.
The phenomenon in which electric current is generated by the varying magnetic field is called electromagnetic induction. (March – 2012)
a) Which law helps to detect the direction of the induced current? State the law.
b) Explain what are eddy currents.
c) Write any two uses of eddy currents.
Answer:
a) Lenz’s law
Lenz’s law states that the polarity of induced emf is such that it tends to produce a current which opposes the change in magnetic flux that produced it.
Mathematically the Lenz’s law can be written as
The negative sign represents the effect of Lenz’s law.
b) When bulk pieces of conductors are subjected to changing magnetic flux, induced currents are produced in them. The flow of current resemble swirling eddies in water. Hence these currents are called Eddy currents.
c) Magnetic braking in trains, Electromagnetic damp-ing, induction furnace, Electric power meters.
Question 6.
Match the following quantities using the analogy between mechanical and electrical quantities. (March – 2013)
i) Mass (M) – Charge (q)
ii) Force Constant (k) – Resistance (R)
iii) Displacement (x) – Max. charge stored (q)
iv) Velocity (v) – Inductance (L)
v) Amplitude of forced oscillation (A) – Reciprocal of capacitance (1/c)
vi) Damping constant (b) – Current (I)
Answer:
i) Mass M – Inductance
ii) Force constant k – Reciprocal of capacitance, (I/C)
iii) Displacement – Charge
iv) Velocìty – Current
v) Amplitude of forced oscillation – Maximum charge stored
vi) Damping constant – Resistance
Question 7.
The generation of emf when the magnetic flux associated with a coil changes is known as electromagnetic induction.
a) Mention the factors on which the self-inductance of a solenoid depends.
b) Calculate the energy stored in an inductor of inductance 50mH when a current of 2 A is passing through it.
c) Two identical loops one of copper and other of aluminium are rotated with same speed in the same magnetic field. In which case the
i) induced emf
ii) induced current will be more and why?
Answer:
a) Coefficient of self-inductance
Hence L depends upon
1) Area of coil
2) Total number of turns of coil
3) Length of coil
4) Permeability of free space
N, B and A are same for both aluminium and copper. Hence induced emf will be same for both aluminium and copper.
ii) Induced current
the resistance of aluminium is larger than copper. Hence more current is induced in copper than aluminium.
Question 8.
Michael Faraday observed that whenever magnetic flux linked with a coil changes, an e.m.f. is induced in the coil. Suppose a coil of ‘N’ turns and radius ‘R’ is kept normal to a varying magnetic field B = BoCoscωt. (Say – 2013)
a) What is the flux linked with the coil at any instant ‘t’?
b) Obtain the e.m.f. induced in the coil.
c) Which law helps to detect the direction of the induced current? State the law.
Answer:
c) Lenz’s law- Lenz’s law states that the polarity of induced emf is such that it tends to produce a current which opposes the change in magnitude flux that produced it.
Question 9.
For many purposes, it is necessary to change an alternating voltage from one value to another. This is done with a transformer. (March – 2014)
a) The basic principle behind a transformer is
b) Give an expression for the voltage and current in a transformer.
Answer:
a) Mutual induction
Question 10.
When the magnetic flux associated with a coil changes an emf is induced in the circuit. (March – 2015)
A) State Faraday’s law of electromagnetic induction.
B) Mention the physical significance of Lenz’s law with an example.
C) When an electrical appliance is switched off, sparking occurs. Why?
Answer:
A) Faraday’s law of electromagnetic induction states that the magnitude of the induced emf in a circuit is equal to the time rate of change of magnetic flux through the circuit.
Mathematically, tfie induced emf is given by
If the coil contain N turns, the total induced emf is given by,
B) Refer Lenz’s law is an accordance with the law of conservation of energy.
C) When an electrical appliance is switched off, an back emf is produced. Due to this back emf, spark is produced.
Question 11.
a) State Faraday’s law of electromagnetic induction. Write its mathematical form. (Say – 2016)
b) Name the factors on w hich the inductance of a coil depends.
Answer:
Magnitude of induced emf in a circuit is equal to the time rate of change of magnetic flux through the circuit.
Number of turns, Area of cross section of coil and permeability of medium.
Question 12.
a) What is eddy current? Mention one application of it. (Say – 2017)
b) An AC source is connected to a coil with negligible resistance and a bulb in series as shown in the figure. If an iron rod is gradually inserted in the coil, what happens to the brightness of the bulb? Explain.
Answer:
a) Whenever the magnetic flux linked with a metal block changes, induced currents are produced. The induced currents flow in a closed path. Such currents are called eddy currents.
Magnetic braking in trains : Strong electromagnets are situated above the rails. When the electromagnets are activated, eddy currents induced in the rails. This eddy current will oppose the motion of the train.
b) When iron rod is inserted in to the coil, the brightness of bulb decreases. When iron rod is inserted, the value of L increases. Hence inductive reactance of the circuit increases. This increase in inductive reactance will decrease the current flowthrough bulb.
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