## Kerala Plus Two Physics Model Question Paper 2

**Time: 2 Hours**

**Cool off time : 15 Minutes**

**General Instructions to candidates:**

- There is a ‘cool off time’ of 15 minutes in addition to the writing time of 2 hrs.
- Your are not allowed to write your answers nor to discuss anything with others during the ‘cool off time’.
- Use the ‘cool off time’ to get familiar with the questions and to plan your answers.
- Read questions carefully before you answering.
- All questions are compulsory and only internal choice is allowed.
- When you select a question, all the sub-questions must be answered from the same question itself.
- Calculations, figures and graphs should be shown in the answer sheet itself.
- Malayalam version of the questions is also provided.
- Give equations wherever necessary.
- Electronic devices except non programmable calculators are not allowed in the Examination Hall.

Questions 1 and 2 carry 1 score each. Answer both.

Question 1.

Electromagnets are made of soft iron because soft iron has

a. low retentivity and high coercive force

b. high retentivity and high coercive force

c. low retentivity and low coercive force

d. high retentivity and low coercive force

Question 2.

Draw the symbol of NOR gate

Answer any six questions from question number 3 to 10. Each question carries 2 scores.

Question 3.

a. The electric field of a plane electromagnetic wave traveling in the +ve Z-direction is described by

a. E_{x} = E_{0} sin (kz + ωt)

b. E_{x }= E_{0} sin (kz – ωt)

c. E_{x} = E_{0} sin (2kz)

d. E_{x} = E_{0} sin (kz)

b. We feel excessive sweating on a cloudy day. Why ?

Question 4.

For many purposes, it is necessary to change an alternating voltage from one value to another. This is done with a transformer.

a. The basic principle behind a transformer is…..

b. Give an expression for the voltage and current in a transformer.

Question 5.

a. Name the physical quantity which has its unit joule coulomb^{-1}. Is it a vector or a scalar?

b. Two plane sheets of charge densities +σ and -σ are kept in air as shown in figure. What are the electric field intensities at point A and B?

Question 6.

Name the electromagnetic waves used for the following applications.

a. Imaging of bones in human body.

b. Mobile phone communication.

c. Remote control of T.V.sets.

d. For sterilizing surgical instruments.

Question 7.

a. Range of an electronic communication system is the

i. distance to the nearest TV station.

ii. distance to the nearest radio station.

iii. largest distance the signal can travel.

iv. largest distance between a source and destination up to which the signal is received with sufficient strength.

b. If the height of TV transmitting antenna is increased its coverage increases. Why?

Question 8.

Match the following in 3 columns.

Question 9.

a. The resistance ‘R’ of a conductor depends on its length ‘I’, area of cross- section ‘A’ and the resistivity of the material ‘ρ’. The correct expression connecting R, I, A and ‘ρ’ is

b. The voltage – current graphs for two resistors of the same material and same radii with lengths L1 and L2 are shown in the figure. If L1 > L2 state with reason, which of these graphs represents voltage current charge for L1?

Question 10.

De Broglie proposed the wave nature of electrons suggesting matter waves.

Find the momentum, speed and de Broglie wavelength of an electron with kinetic energy of 120 eV.

Answer any five questions from question number 11 to 16. Each question carries 3 scores.

Question 11.

a. The work function of a metal is 6 eV. If two photons each having energy 4 eV strike with the metal surface

i. will the emission be possible ?

ii. why ?

b. The waves associated with matter is called matter waves. Let λ_{e} and λ_{p} be the de- Broglie wave lengths associated with electron and proton respectively. If they are accelerated by same potential, then

Question 12.

The region around a charge where its effect can be felt is called the electric field.

a. The electric field lines corresponding to an electric field is shown below.

b. Some equipotential surfaces are shown in the figure. What can you say about the magnitude and direction of the electric field ?

Question 13.

Given below is the graph between frequency (υ) of the incident light and maximum kinetic energy (E_{k}) of emitted photoelectrons.

a. Define the terms – work functions and threshold frequency.

b. Find the values of

i. threshold frequency and

ii.work function from the graph

Question 14.

Consider the logic circuit using NOR gates given below:

a. Write the truth table for the circuit.

b. Identify the logic operation which this circuit is performing.

Question 15.

The phenomenon in which electric current is generated by varying magnetic field is called electromagnetic induction.

a. Which law helps to detect the direction of induced current? State the law.

b. Explain what are eddy currents.

c. Write any two uses of eddy currents.

Question 16.

Biasing is provided for maintaining proper current flow across a p-n junction.

a. In a biased p-n junction the net flow of holes is from ‘n’ region to ‘p’ regional

b. For the device shown below draw the V-I characteristics when the potential is applied between the terminals A and B.

Answer any four questions from question number 17 to 21. Each question carries 4 scores.

Question 17.

a. Find the equivalent resistance of the circuit.

b. Determine the current through the 75Ω resistance.

Question 18.

a. A convex lens

i. is thicker at the edges than at the middle.

ii. is thicker at the middle than at the edges.

iii. diverges rays of light.

iv. is of uniform thickness everywhere.

b. With the help of a ray diagram sketch the image formation of a convex lens when the object is between C and F.

c. Derive the lens maker’s formula.

Question 19.

Remya makes the following circuit to measure the emf of a cell.

She says that the voltmeter reading will give the emf of the cell.

a. The Physics teacher says that it is not :possible to measure the emf of the cell in this way. Justify this statement.

b. Explain with a circuit diagram the method to measure the emf of a cell with a potentiometer if you are given another standard cell, (whose e.m.f. is known)

Question 20.

a. What do you mean by Q value of a nuclear reaction?

b. Write down the expression for Q value in the case of α decay.

c. Two nuclei have mass numbers in the ratio 1 : 64. What is the ratio of their nuclear radii ?

Question 21.

A capacitor is a device used for storing charge as well as energy. It is based on a property called capacitance.

a. Write the SI unit of capacitance and define it.

b. You are given two capacitors of 2µF and 3µF. What are the maximum and minimum values of capacitance that can be obtained by combining them?

c. Obtain an expression for the electrostatic energy stored in a capacitor.

Answer any three questions from question number 22 to 25. Each question carries 5 scores.

Question 22.

To emit a free electron from a metal surface a minimum amount of energy must be supplied.

a. This energy is called …….

b. State three methods to supply this energy to the free electron.

c. When light of frequency 7.21×10^{14} Hz is incident on a metal surface, the maximum speed of the ejected electrons is 6×10^{5} m/ s. Calculate the threshold frequency for the metal.

Question 23.

Figure shows a graph between angle of incidence and the respective deviation of light when it is passed through an optical element.

a. Name this optical element.

b. What will happen to the angle of minimum deviation D if it is completely immersed in water? Justify your answer.

c. Obtain an expression for the refractive index of the material of this optical element.

Question 24.

The idea of ‘Electric field lines ’ is useful in pictorially mapping the electric field around charges.

a. Give any two properties of electric lines of force.

b. State Gauss’s theorem in electrostatics.

c. Using the theorem, derive an expression for electric field due to a uniformly charged spherical shell.

i. at a point outside the shell

ii. at a point inside the shell

d.

A point charge of +10 μc is at a distance of 5cm directly above the centre of a square of side 10 cm as shown in the figure. What is the electric flux through the square?

Question 25.

Gauss’s law can be used to determine the electric field due to a charge distribution, a. Below are some statements about Gauss’s law. Say whether they are true or false.

i. Gauss’s law is valid only for symmetrical charge distributions.

ii. The electric field calculated by Gauss’s law is the field due to charges inside the Gaussian surface.

b. Apply Gauss’s law to find the electric field due to an infinitely long plane sheet of charge.

c. “There can be no net charge in a region in which the electric field is uniform at all points”. Do you agree with this statement? Justify your answer.

**Answers**

Answer 1.

d

Answer 2.

Answer 3.

a. b. E_{x }= E_{0 }sin (kz – ωt)

b. The clouds prevents IR radiation from passing through and thus keeps the earth’s surface warm.

Answer 4.

a. Mutual induction

Answer 5.

a. Electric potential. It is a scalar quantity.

Answer 6.

a. x-rays

b. Radio waves

c. Infrared rays

d. Ultraviolet rays

Answer 7.

a. iv. largest distance between a source and destination up to which the signal is received with sufficient strength.

b. We know range, d = √2hR ; Where h is the height of the antenna. Therefore increasing height increases the range ie., coverage.

Answer 8.

Answer 9.

a. \(R=\frac { pl }{ A }\)

b. B represents voltage change for L. Resistance of B is greater than that for A, since resistance increases with length.

Answer 10.

De Broglie wavelength of electrons

from V², we can calculate V so we get the value of P also.

Answer 11.

a. (i) No

(ii) Free electrons are bound to the metal with some force. The minimum energy j required to liberate an electron from the metal is called work function, here the energy of one photon is less than work function. So emission will not be possible.

b. (i) λ_{e} > λ_{p}

Answer 12.

a. E_{A} = E_{C} > E_{B}

b. The direction of electric field at any point on the equatorial line of the dipole will be opposite to the dipole moment. The magnitudes of electric fields are equal

Answer 13.

a. Work functions: It is the minimum amount of energy required by an electron to just escape from the metal surface of the metal.

Threshold frequency: The minimum value of the frequency of incident radiation which can emit photo electrons from a material.

b. i.Threshold frequency,v_{0} = 10 x 10^{14} Hz

ii. Work function = hv_{0}

= 6.63 x 10^{-34 }x 10 x 10^{14}

= 6.63 x 10^{-19} J

Answer 14.

a. Truth Table

Answer 15.

a. Lenz’s law. This law states that the direction of the induced e.m.f or current is such as to oppose the cause that produced it

b. The currents induced in the body of a conductor, when the magnetic flux linked with the conductor changes are called eddy currents or Focault’s currents

c. i. Electric Brakes

ii. Speedometer

Answer 16.

a. Reverse

Answer 17.

Answer 18.

a. ii. is thicker at the middle than at the edges.

Answer 19.

a. The voltmeter reads terminal potential difference. Emf cannot be measured in this way since the cell is connected to a resistance. Emf is the potential different across the terminals of a cell in a open circuit.

Answer 20.

a. The disintegration energy or the Q- value of a nuclear reaction is the difference between the initial mass energy and the total mass energy of the decay products.

b. For α -decay

Answer 21.

a. SI unit of capacitance is farad. Capacity of a conductor is said to be one farad if one coulomb of charge on it raises its potential by one volt.

b. If the capacitors are in series,

Answer 22.

a. Work function.

b. Thermionic emission, field emission and photo electric emission.

c. u = 7.21 x 10^{14} Hz, V = 6 x 10^{5} m/s

Answer 23.

a. Prism

b. The angle of minimum deviation decreases.

Refractive index of glass with respect to water is 1.5. But refractive index of glass with respect to water is 1.33.

c.

Answer 24.

a. i. Electric lines of force will never intersect.

ii.The tangent to the line of force at any point gives the direction of electric field at that point.

b. The electric flux through any closed surface in free is equal to 1/ε_{0} times the total charge enclosed by the surface.

Answer 25.

a. i. False

ii. False

c. Yes, there can be no net charge in a region in which the electric field is uniform at all points. Consider a region with uniform electric field and a cubical gaussian surface in it whose face is perpendicular to electric field. Now from one face electric field enters which is considered to be +ve from the possible face it gets out which is considered to be -ve. So net flux through the gaussian surface is zero.