CLASS - XII PHYSICS (Unit Magnetic Effects of Current)
CLASS - XII PHYSICS (Unit –Magnetic effects of current)
1 / / [1]2 / A cyclotron is not suitable to accelerate electron. Why? / [1]
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4 / Can neutrons be accelerated in a cyclotron. Why? / [1]
5 / Which physical quantity has the unit wb/m2. Is it a scalar or vector quantity? / [1]
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16 / State Ampere’s circuital law. Write the expression for the magnetic field at the centre of a circular coil of readius R carrying a current l. Draw the magnetic field lines due to this coil. / [3]
17 / Write the expression for the force acting on a charged particle of charge q moving with velocity in the presence of magnetic field . Show that in the presence of this force:
(i)the kinetic energy of th particle does not change
(ii)its instantaneous power is zero. / [3]
18 / A circular coil of 200 turns and radius 10 cm is placed in a uniform magnetic field of 0.5 T, normal to the plane of the coil. If the current in the coil is 3.0 A, calculate the
(a)total torque on the coil
(b)total force on the coil.
(c)Average force on each electron in the coil, due to the magnetic field.
Assume the area of cross-section of the wire to be 10-5m2 and the free electron density is 1029/m3. / [3]
19 / Deduce the expression for the torque experienced by a rectangular loop carrying a steady current ‘l’ and placed in a uniform magnetic field . Indicate the direction of the torque acting on the loop. / [3]
20 / Depict the field-line pattern due to a current carrying solenoid of finite length.
(i)In what way do these lines differ from those due to an electric dipole?
(ii)Why can’t two magnetic field lines intersect each other? / [3]
21 / A rectangular loop of wire of size 4 cm X 10 cm carries a steady current of 2 A. A straight long wire carrying 5 A current is kept near the loop as shown. If the loop and the wire are coplanar find (i) the torque acting on the loop and (ii) the magnitude and direction of the force on the loop due to the current carrying wire.
/ [3]
22 / Draw a labeled diagram of a moving coil galvanometer and explain its working. What is the function of radial magnetic field inside the coil? / [3]
23 / Sandeep’s mother had put lot of clothes for washing in the washing machine, but the machine did not start and an indicator was showing that the lid did not close. Sandeep seeing his mother disturbed thought that he would close the lid by force but realized the mechanism was different. It was a magnetic system. He went to the shop and got a small magnetic door closer and put it on the lid. The machine started working. His mother was happy that Sandeep helped her to save Rs. 500/- also.
- What was the value developed by Sandeep?
- What values did his mother impart to Sandeep?
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25 / (a)Derive an expression for the force per unit length experienced by two infinitely long straight parallel wires, carrying currents in the same direction.
(b)(i) use the above to define one ampere
(ii) show that the oppositely directed parallel currents repel whereas currents flowing in the same direction attract. / [5]
26 / (a)Write the expression for the force, , acting on a charged particle of charge ‘q’, moving with a velocity in the presence of both electric field and magnetic field . Obtain the condition under which the particle moves undeflected through the fields.
(b)A rectangular loop of size l x b carrying a steady current is placed in a uniform magnetic field . Prove that the torque acting on the loop is given by = x where is the magnetic movement of the loop. / [5]