# Plus Two Physics Model Question Paper 3

## Kerala Plus Two Physics Model Question Paper 3

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 – 7 carry 1 score each. Answer any six questions.

Question 1.
Potentiometer measures potential more accurately because

a. It measures potential in the open circuit
b. It uses sensitive galvanometer for null deflection
c. It uses high resistance potentiometer wire
d. It measures potential in the closed circuit

Question 2.
Tesla is the unit of

Question 3.
Write the time constant of C-R circuit ?

Question 4.
Green-house effect is the heating up of earth atmosphere due to____
a. green plants
b.infra-red rays
c. x-rays
d. ultraviolet rays

Question 5.
Rainbow is formed due to a combination of

a. dispersion and total internal reflection
b. refraction and absorption
c. dispersion and focusing
d. refraction and scattering

Question 6.
Ratio of intensities of two waves are given by 4:1. Then find the ratio of the amplitudes of the two waves.

Question 7.
The spectrum obtained from a sodium vapor lamp is an example of

a. band spectrum
b. continuous spectrum
c. emission spectrum
d. absorption spectrum

Questions 8 to 15 carry 2 score each. Answer any 7 questions.

Question 8.
Copper is one of the suitable materials to make connecting wires due to its low resistivity.
a. What do you mean by resistivity?
b. A copper wire is in the form of a cylinder and has a resistance R. It is stretched till its thickness reduces by half of its initial size. Find its new resistance in terms of R.

Question 9.
It was james Clark Maxwell who modified Ampere’s circuital theorem by introducing the concept of displacement current.

a. What do you mean by displacement current?

Question 10.
Match the following

Question 11.
A body of mass m is charged negatively. State whether the following statements are true or false.
a. During charging, there is change in mass of the body.
b. The body can be charged to 2.5 e where e is the charge of an electron.
c. While charging the body by induction new charges are created in it.
d. The force between two charged object is less when there is a medium between them (than in vacuum).

Question 12.
a. A receiver in a communication system must have
i. pick-up antenna
ii. demodulator
iii. amplifier
iv. all of these
b. Which of the following statements is wrong?
i. The attenuation of surface waves in creases with increase in frequency.
ii. The phenomenon involved in sky wave propagation is similar to total internal reflection.
iii. Space wave mode of propagation is used in satellite communication.
iv. Sky wave propagation is useful only in the range of frequencies 30 MHz to 40 MHz.

Question 13.
a. The core of a transformer has the following properties :
i. core is laminated.
ii. hysterisis loop is narrow.
Explain the significance of each property.
b. What is meant by resonance in an LCR circuit ?

Question 14.
a. Permanent magnets should have
i. high retentivity and low coercivity.
ii. low retentivity and high coercivity.
iii. high retentivity and high coercivity.
iv. low retentivity and low coercivity.
b. Distinguish between Para, Ferro an Dia magnetism.

Question 15.

a. From the above figures which one corresponds to a typical semiconductor.
b. Dimension of temperature coefficient α is……..

Questions 16 to 22 carry 3 score each. Answer any 6 questions.

Question 16.
a. Work function of a metal is the
i. energy required by an electron to get absorbed in the metal surface.
ii. minimum energy required by an electron to escape from the metal surface.
iii. energy required by an electron to be retained in the metal surface.
iv. maximum energy required by an electron to escape from the metal surface.
b. Write Einstein’s Photo-Electric Equation and explain the terms in it.
c. All Photo electrons are not emitted with the same energy as the incident photons. Why?

Question 17.
Kirchhoff’s rules are very useful for analysis of electrical circuits.
a. State Kirchhoff s junction rule.
b. Find the effective resistance of the circuit given below :

Question 18.
A fascinating behaviour of the series RLC circuit is the phenomenon of resonance.
a. Explain Resonance in an LCR circuit.
b. Draw a graphical representation of variation of current amplitude in im with frequency to ω
c. What do you mean by sharpness of resonance? Explain it.

Question 19.
a. When a low flying aircraft passes over head, we sometimes notice a slight shaking of the picture on our TV screen. Identify the optical phenomenon behind it.
b. In electromagnetic spectra, the wave length and frequencies are inversely related. A radio can tune into any station in the 7.5 MHz to 12 MHz band. Determine the corresponding wavelength band

Question 20.
Various propagation modes are used in communication.
a. Mention two communication system that uses space wave propagation.
b. Why modulation is necessary in communication ?
c. If a signal of frequency cos is used to ωs modulate a carrier wave of frequency ωc
which are the frequencies contained in the modulated signal other than ωc?

Question 21.
Match the following quantities using the analogy between mechanical and electrical quantities.

Question 22.
In a nuclear reactor the chain reaction is carried out under controlled conditions.
a. Name the material that is used as control rods in a nuclear reactor.
b. Average energy of a neutron produced in fission of 92235U nucleus is…….
c. Write down the reactions involved in the conversion of to 92238U to 94239Pu in a nuclear reactor

Questions from 23 – 26 carry 4 scores. Answer any 3 questions.

Question 23.
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 7.21×1014 Hz is incident on a metal surface, the maximum speed of the ejected electrons is 6×105 m/s. Calculate the threshold frequency for the metal.

Question 24.
Seema constructed a series LCR circuit in the laboratory as shown in the diagram. She found that the voltages across the inductor and capacitor are equal when the circuit is connected to an ac source.

a. State the condition at which the voltages across L and C become equal.

b. Obtain an expression for the frequency at which this situation occurs in a series LCR circuit.

c. Find the voltmeter and ammeter readings in the circuit.

Question 25.
Brewster’s law gives a relationship between angle of polarisation and refractive index of the material.

a. State Brsewster’s law

b. A ray of light is allowed to incident on the surface of a glass plate and it is found that the reflected and refracted rays are mutually perpendicular as shown in the figure. The refracted ray is deviated from its initial path by an angle of 30°
Determine the refractive index of the glass plate.

Question 26.
a. A ray of light travels from a denser to a rarer medium then, the ray
i. doesn’t bend at all.
ii. bends towards the normal.
iii. bends away from the normal.
iv. goes along the normal.
b. Draw a diagram showing the path of a monochromatic light through a triangular prism.
c. Using this diagram obtain the relation

Questions from 27 – 29 carry 5 scores. Answer any 2 questions.

Question 27.
a. What do you mean by barrier potential of a diode ?
b. With the help of a diagram explain the working of a full wave rectifier.

Question 28.
Various phenomena exhibited by light can be explained using the wave theory of light.
a. Name the phenomenon which proves the transverse nature of light.
b. What are the differences between interference and diffraction?
c. A plane wave front is incident on a single slit. Discuss the diffraction pattern formed by the slit. Represent the variation of intensity graphically.

Question 29.
A moving charge can produce a magnetic field.
a. How does a current loop behaves like a magnetic dipole ?
b. Draw the magnetic field lines for a current loop to support your answer.
c. i. What is a cyclotron ?
ii. Write down the expression for cyclotron frequency.

a

magnetic field

CR

b

a

c

a. Resistivity of the material of a conductor is defined as the resistance of the conductor of unit length and of unit area of cross-section.

a. Displacement current is that current which comes into existence, in addition to the conduction current whenever the electric flux changes with time.
b. Ampere

a. true
b. false
c. false
d. true

a. (iv) all of these
b. (iv) Sky wave propagation is useful only in the range of frequencies 30 to 40MHz

a. (i) For reducing eddy current. Eddy current heats the core and energy will be lost.
(ii) For reducing hysterisis loss.
b. In LCR, at a particular frequency XL = XC. This condition is called resonance. This frequency is called resonance frequency.

a. iii. high retentivity and high coercivity.
b. Paramagnetism: Feebly magnetise along applied field.
Diamagnetism: Feebly magnetise opposite to magnetic field.
Ferromag netism: Strongly magnetise along magnetic field.

a. Fig.(2)
b. α = coefficient of temp

a. ii. minimum energy required by an electron to escape from the metal surface.

c. All the photoelectrons emitted from the metal do not have the same energy. Photoelectric current is zero when the stopping potential is sufficient to repel | even the most energetic photoelectrons, with the maximum kinetic energy (Kmax),So that Kmax = eV0

a. In an electric circuit, the sum of currents | entering the junction is equal to the sum of currents leaving the junction.
b. Here 3Ω, 6Ω are parallel and 6Ω and 12Ω are parallel.

a. In LCR, at a particular frequency XL = XC. This frequency is called resonance frequency.

c. Sharpness of resonance is depends of quality factor or Q factor.
Q factor is equal to the ratio inductive reactance or capacitative reactance to the impedence at resonance.

a. Interference

b. 1. Size of the antenna: We need an antenna having a size comparable to the wave length of the signal.
2. Effective power radiated by antenna,

a. Work function.
b. Thermionic emission, field emission and photo electric emission.

a. p.d across L and C are equal when inductive reactance = Capacitive reactance (XL = XC), i.e., at resonance.
b. At resonance, XL = XC

a. Tangent of angle of polarization is equal to the reflective index.
b. i + r = 90°
θ + r = 90°
θ = 90° – r = 90 – 30 = 60°
n = tan 60° = √3 = 1.732

a. iii bends away from the normal
b.

a. During the formation of a p-n junction, holes diffuse from p to n side and electrons diffuse from n to p side. Thus there is excess of positively charged ions in n side and negatively charged ions in p side. This sets up a potential difference across the junction which is called barrier potential. It stops further diffusion.

• During +ve half cycle of a.c, the end A is positive and end B is negative with respect to the centre tap. Diode D1 gets forward biased and conducts current while D2 is reverse biased and does not conduct.
• During -ve half cycle, the end Abe comes negative and end B becomes positive with respect to the centre tap. The diode D gets reverse biased and does not conduct. The diode D2 gets forward biased and conducts current.
• The output current is unidirectional and pulsating which may be filtered by connecting a capacitor parallel to load RL.