Class XII Physics

Chapter 1 - Electric Charges & Fields

Chapter 2 - Electrostatic Potential and Capacitance

Chapter 3 - Current Electricity

Chapter 4 - Moving Charges & Magnetism

Chapter 5 - Magnetism & Matter

Chapter 6 - Electromagnetic Induction

Chapter 7 - Alternating Current

Chapter 8 - Electromagnetic Waves

Chapter 9 - Ray Optics & Optical Instruments

Chapter 10 - Wave Optics

Chapter 11 - Dual Nature of Radiation and Matter

Chapter 12 - Atoms

Chapter 13 - Nuclei

Chapter 14 - Semiconductor Electronics : Materials, Devices and Simple Circuits

Model Test Paper

Q1 If the net electric flux through a closed surface is zero, then we can infer

a. no net charge is enclosed by the surface

b. uniform electric field exists within the surface

c. electric potential varies from point to point inside the surface

d. charge is present inside the surface

Q2 An electric dipole consisting of charges +q and -q separated by a distance L is in stable equilibrium in a uniform electric field E. The electrostatic potential energy of the dipole is 

a. qLE

b. zero

c. -qLE

d. -2qEL

Q3 A potentiometer can measure emf of a cell because

a. the sensitivity of potentiometer is large

b. no current is drawn from the cell at balance

c. no current flows in the wire of potentiometer at balance

d. internal resistance of cell is neglected. 

Q4 Two resistors R1 and R2 of 4 ohm and 6 ohm are connected in parallel across a battery. The ratio of power dissipated in them, P1:P2 will be 

a. 4:9

b. 3:2

c. 9:4

d. 2:3

Q5 The magnetic dipole moment of a current carrying coil does not depend on 

a. no. of turns of the coil

b. cross-sectional area of the soil

c. current flowing in the soil

d. material of the turns of the soil

Q6 Larger aperture of objective lens in an astronomical telescope

a. increase the resolving power of telescope

b. decrease the brightness of the image

c. increases the size of the image

d. decreases the length of the telescope

Q7 A biconvex lens of glass having refractive index 1.47 is immersed in a liquid. It becomes invisible and behaves as a plane glass plate. The refractive index of the liquid is 

a. 1.47

b. 1.62

c. 1.33

d. 1.51

Q8 For a glass prism, the angle of minimum deviation will be smallest for the light of 

a. red colour

b. blue colour

c. yellow colour

d. green colour

Q9 Which of the following statements is not correct according to Rutherford model?

a. Most of the space inside an atom is empty

b. The electrons revolve around the nucleus under the influence of coulomb force acting on them

c. Most part of the mass of the atom and its positive charges are concentrated at its centre

d. The stability of atom was established by the model

Q10 Photons of energies 1eV and 2eV are successively incident on a metallic surface of work function 0.5eV. The ratio of kinetic energy of most energetic photoelectrons in the two cases will be

a. 1:2

b. 1:1

c. 1:3

d. 1:4

Q11 The magnetic field and angle of dip at a place on the earth are 0.3G and 30 degrees, respectively. The value of vertical component of the earth's magnetic filed at the place is

Q12 Laminated iron sheets are used to minimize _ _ _ _ currents in the core of a transformer

Q13 The no. of turns of a solenoid are doubled without changing its length and area of cross-section. The self-inductance of the solenoid will become _ _ _ _ times.

Q14 According to Bohr's atomic model, the circumference of the electron orbit is always an _ _ _ _ multiple of de Broglie wavelength.

Q15 A ray of light on passing through an equilateral glass prism, suffers a minimum deviation equal to the angle of the prism. The value of refractive index of the material of the prism is _ _ _ _ .

Q16 Write the mathematical form of Ampere-Maxwell circuital law. 

Q17 How does an increase in doping concentration affect the width of depletion layer of a p-n junction diode?

Q18 The nuclear radius of 27 Al 13 of 3.6 fermi. Find the nuclear radius of 64Cu29.

or 

A proton and an electron have equal speeds. Find the ratio of de Broglie wavelengths associated with them. 

Ans. 28 

a. 

Let V is the potential difference between B1 and B2

Putting equation (2) and (3) in (1)

If we replace this with a single cell it can be written as 

Then,

b. 

Ans. 29   

a.

b. 

Due to the current element  considered at A the magnetic field at P is- 

Consider a current element opposite to A, that is at B, then we can see that the y components of the magnetic, field due to this current element cancel and X component is only present.

So we can say that the net magnetic field is along the X-direction.

The net magnetic field at P is

Ans. 29   or part

a. current sensitivity of a galvanometer is defined as deflection per unit current flowing through it. 

b. 

i. by connecting a shunt parallel to the galvanometer

(ii) 

Ans. 30

a. The peak value of the current through the circuit

i. 

ii. 

In RC series circuit the current leads the applied voltage.

Ans. 31

a. Fringe width β  ∝ D. Therefore the fringe width increases when D is increase. 

b. β  ∝ 1/ d, therefore when d is increased the fringe width decreases

c. If s is the size of the source and S is distant of the source from the plant of the two slits, then for interference fringes to see, the condition is 

Ans. 32 

(a) Speed of light

(b) 

i. Microwave 1mm to 0.1 m

ii. Infrared wave 1 mm to 700nm

Ans. 33

Energy released, Q = [M (231X) + M (4He) – M(235 Y)]c2 

= [(7.835 × 231) + (7.07 × 4) – (7.8 × 235)]MeV 

= [1809.9 + 28.28 – 1833] MeV 

= 5.18 MeV = 5.18 × 1.6 × 10–13 J 

This entire kinetic energy is taken by -particle as given

Ans. 34 (a)

If the input voltage increases, the current through Rsand Zener diode also increases. This increases the voltage drop across Rs without a change in the voltage across the Zener diode. This is because, in the breakdown region, Zener voltage remains constant even though the current through that Zener diode varies. 

(b) Heavy doping of p and n side of a zener is done to decrease the width of the depletion region which increases the electric field at the junction.

Ans. 35 

(i) 0 < x < R

Inside a spherical shell, the charge = 0, therefore, the electric field E = 0

ii) x>R 

Consider a point P outside the shell at a distance r. Consider a spherical Gaussian surface of radius r. 

Then by Gauss law: 

Flux enclosed by the surface

b). i. The net outward flux = 2EA

ii) The net charge present inside the cylinder

Ans. 35 or part

Work done in bringing q1 from infinity against the electric field

Work done in bringing q2 from infinity against the electric field

Work done on Q2 against the field due to Q1

The potential energy of the system= Total work done in assembling the system

b. 

c. Work done= charge in potential energy

Ans. 36 Let us consider a loop ABCD in a uniform magnetic field of strength B. and Let the current through the loop be I. 

Magnetic forces of AB and CD are equal and opposite and have a different line of action so constitutes torque.

lb=A 

The radius of the circular path 

Ans 36         or part

Transformer works on the principle of mutual induction.

\rightarrow whenever the current associated with the primary coil charges an emf is induced in the secondary coil.

A transformer in which the output (secondary) voltage is greater than its input (primary) voltage is called a step-up transformer.

The induced emf across the primary

The induced emf across the secondary

i)Transformer cores are laminated to reduce the eddy current

ii)Thick copper wires are used to reduce the heat loss

b)i.

ii.