PUC Science 2nd PUC Class 12 - Karnataka Board PUC Question Bank Solutions

Figure shows a conducting circular loop of radius a placed in a uniform, perpendicular magnetic field B. A thick metal rod OA is pivoted at the centre O. The other end of the rod touches the loop at A. The centre O and a fixed point C on the loop are connected by a wire OC of resistance R. A force is applied at the middle point of the rod OAperpendicularly, so that the rod rotates clockwise at a uniform angular velocity ω. Find the force.

Let i_E, i_C and i_B represent the emitter current, the collector current and the base current respectively in a transistor. Then
(a) i_C is slightly smaller than i_E
(b) i_C is slightly greater than i_E
(c) i_B is much smaller than i_E
(d) i_B is much greater than i_E.

In a normal operation of a transistor,
(a) the base−emitter junction is forward-baised
(b) the base−collector junction is forward-baised
(c) the base−emitter junction is reverse-baised
(d) the base−collector junction is reverse-baised.

An α-particle is bombarded on ¹⁴N. As a result, a ¹⁷O nucleus is formed and a particle is emitted. This particle is a

Find the energy liberated in the reaction
²²³Ra → ²⁰⁹Pb + ¹⁴C.
The atomic masses needed are as follows.
²²³Ra         ²⁰⁹Pb        ¹⁴C
22..018 u  208.981 u  14.003 u

Calculate the minimum energy needed to separate a neutron from a nucleus with Zprotons and N neutrons it terms of the masses M_Z.N' M_Z,N−1 and the mass of the neutron.

³²P beta-decays to ³²S. Find the sum of the energy of the antineutrino and the kinetic energy of the β-particle. Neglect the recoil of the daughter nucleus. Atomic mass of ³²P = 31.974 u and that of ³²S = 31.972 u.

In the decay ⁶⁴Cu → ⁶⁴Ni + e⁺ + v, the maximum kinetic energy carried by the positron is found to be 0.650 MeV.
(a) What is the energy of the neutrino which was emitted together with a positron of kinetic energy 0.150 MeV?
(b) What is the momentum of this neutrino in kg m s⁻¹?
Use the formula applicable to a photon.

Carbon (Z = 6) with mass number 11 decays to boron (Z = 5). (a) Is it a β⁺-decay or a β⁻decay? (b) The half-life of the decay scheme is 20.3 minutes. How much time will elapse before a mixture of 90% carbon-11 and 10% boron-11 (by the number of atoms) converts itself into a mixture of 10% carbon-11 and 90% boron-11?

How is polarisation of light obtained by scattering of light?

Two identical parallel plate capacitors A and B are connected to a battery of V volts with the switch S closed. The switch is now opened and the free space between the plates of the capacitors is filled with a dielectric of dielectric constant K. Find the ratio of the total electrostatic energy stored in both capacitors before and after the introduction of the dielectric.

(i) Find equivalent capacitance between A and B in the combination given below. Each capacitor is of 2 µF capacitance.

(ii) If a dc source of 7 V is connected across AB, how much charge is drawn from the source and what is the energy stored in the network? 

Why is it necessary to introduce a radial magnetic field inside the coil of a galvanometer?

Can a galvanometer as such be used for measuring the current? Explain.

Two identical capacitors of 12 pF each are connected in series across a battery of 50 V. How much electrostatic energy is stored in the combination? If these were connected in parallel across the same battery, how much energy will be stored in the combination now?

Also find the charge drawn from the battery in each case.

State the underlying principle of working of a moving coil galvanometer. Write two reasons why a galvanometer can not be used as such to measure current in a given circuit. Name any two factors on which the current sensitivity of a galvanometer depends.

Three identical capacitors C₁, C₂ and C₃ of capacitance 6 μF each are connected to a 12 V battery as shown.

Find

(i) charge on each capacitor

(ii) equivalent capacitance of the network

(iii) energy stored in the network of capacitors

The muscles of a normal eye are least strained when the eye is focussed on an object

When objects at different distances are seen by the eye, which of the following remain constant?