Physics (Theory) Set 1 2018-2019 ISC (Commerce) Class 12 Question Paper Solution

 A closed surface in vacuum encloses charges –q and +3q. The total electric flux emerging out of the surface is :

 Zero 

`(2q)/∈_0`

`(3q)/∈_0`

`(4q)/∈_0`

What is the angle of dip at a place where the horizontal component `(B_H)` and vertical component `(B_V)` of earth’s magnetic field are equal : 

 130° 

60° 

 45° 

 90° 

A beam of light is incident at the polarizing angle of 35° on a certain glass plate. The refractive index of the glass plate is : 

sin 35° 

 tan 35° 

 tan 55° 

sin 55° 

In a gamma ray emission from nucleus : 

 only the number of protons change 

 the number of protons and neutrons, both change 

 there is no change in the number of protons and the number of neutrons 

only the number of neutrons change 

The energy associated with light of which of the following colours is minimum : 

violet

red

 green 

yellow

Define equipotential surface. 

Calculate the net emf across A and B shown in Figure 1 below :

Why are the pole pieces of a horseshoe magnet in a moving coil galvanometer made cylinder in shape? 

What is the value of power factor for a pure resistor connected to an alternating current source ? 

What should be the path difference between two waves reaching a point for obtaining constructive interference in Young’s Double Slit experiment ?

Define critical angle for a given medium.

Name the series in the atomic spectra of the hydrogen atom that falls in the ultra violet region. 

In a potentiometer experiment, the balancing length with a resistance of 2Ω is found to be 100 cm, while that of an unknown resistance is 500 cm. Calculate the value of the unknown resistance. 

A rectangular loop of area 5m2, has 50 turns and carries a current of 1A. It is hold in a uniform magnetic field of 0.1T, at an angle of 30°. Calculate the torque experienced by the coil. 

An electric current I flows through an infinitely long conductor as shown in Figure 2 (a) below. Write an expression and direction for the magnetic field at point P. 

An electric current I flows through a circular loop as shown in Figure 2(b) below. Write an expression and direction for the magnetic field at the centre of the loop at point P.

A transformer is used to step up an alternating emf of 200V to 440V. If the primary coil has 1000 turns, calculate the number of turns in the secondary coil. 

This is an example of step-up transformer.

Write any one use for each of the following mirrors : 

(a) Convex

(b) Concave 

The deviation produced for violet, yellow and red lights for crown glass are 3.75°, 3.25° and 2.86° respectively. Calculate the dispersive power of the crown glass.

What is mass defect?

What conclusion is drawn from Rutherford’s scattering experiment of α-particles?

Define the following with reference to photoelectric effect : 

(a) Threshold frequency (`f_0`)

(b) Stopping potential (`V_s`)

The half-life of radium is 1550 years. Calculate its disintegration constant (`lambda`) . 

Copy and complete the following table for a radioactive element whose half-life is 10 minutes. Assume that you have 30g of this element at t = 0.

Define frequency modulation and state any one advantage of frequency modulation (FM) over amplitude modulation (AM). 

Obtain an expression for electric potential ‘V’ at a point in an end-on position i.e. axial position of the electric dipole. 

Three capacitors of capacitance `C_1 = 3muf` , `C_2 = 6muf` , `C_3 = 10muf` , are connected to a 10V battery as shown in figure 3 below : 

Calculate :

(a) Equivalent capacitance.

(b) Electrostatic potential energy stored in the system 

Obtain the balancing  condition for the Wheatstone bridge arrangements as shown in Figure 4 below:

Draw a labelled circuit diagram of a potentiometer to measure the internal resistance ‘r’ of a cell. Write the working formula (derivation is not required). 

A ray of light is incident on a prism whose refractive index is 1.52 at an angle of 40°. If the angle of emergence is 60°, calculate the angle of the prism. 

Calculate the focal length of a convex lens whose radii of curvature of two surfaces is 10 cm and 15 cm respectively and its refractive index is 1.5. 

Derive the law of reflection using Huygen’s Wave Theory. 

State any two Bohr’s postulates and write the energy value of the ground state of the hydrogen atom. 

With reference to semi-conductors answer the following : 

(i) What is the change in the resistance of the semi-conductor with increase in temperature ?

(ii) Name the majority charge carriers in n-type semi-conductor.

(iii) What is meant by doping ?

(i) An alternating emf of 200 V, 50 Hz is applied to an L-R ciruit, having a resistance R of 10 Ω and an  inductance L of 0.05H connected in series. Calculate : 

(1) Impedance

(2) Current flowing in the circuit 

(ii) Draw a labelled graph showing the variation of inductive reactance (`X_L`) verses frequency (`f`) .

(i) An a.c. source of emf ε = 200 sin omegat is connected to a resistor of 50 Ω . calculate : 

(1) Average current (`"I"_("avg")`)

(2) Root mean square (rms) value of emf 

(ii) State any two characteristics of resonance in an LCR series circuit. 

Draw a neat labelled ray diagram showing the formation of an image at the least distance of distinct vision D by a simple microscope. When the final image is at D, derive an expression for its magnifying power at D. 

Draw a neat labelled diagram of Young’s Double Slit experiment. Show that `beta = (lambdaD)/d` , where the terms have their usual meanings (either for bright or dark fringe).

(i) Draw a labelled circuit diagram of a half wave rectifier and give its output waveform.

(ii) Draw a symbol for NOR gate and write its its truth table. 

(i) Draw a neat circuit diagram to study the input and output characteristics of a common emitter transistor.

(ii) Draw the symbol for AND gate and write its truth table.