CBSE Class 12 Physics Sample Paper Half Yearly 2020

CBSE Class 12 Physics Sample Paper Half Yearly 2020

Half Yearly Examination (2020)

Class-XII

Subject: Physics

Time: 3:00 hour

M.M.: 70

Note: Section A contains 20 questions of 1 mark each,  Section B contains 7 questions of 2 marks each, Section C contains 7 questions of 3 marks each, Section D contain 3 questions of 5 marks each.All questions are compulsory.

SECTION-A

1- The velocity of electron which causes the current is:

i) Thermal velocity

ii) drift velocity

iii) Average velocity

iv) None

2- Ohm’s Law is only valid for:

i) Metallic conductors

ii) Non metallic conductors.

iii) electrolytes

iv) None

3- The electric flux over the surface of a sphere if it is charged with 10 Micro coulomb

i) 36π×10⁴ Nm²/c

ii) 36π×10^-4Nm²/c

iii) 36 π×10⁶Nm²/c

iv) 36π×10^-6Nm²/c

4- The intensity of electric field at any point on the surface of a charged conductor

i) zero

ii) perpendicular to the surface

iii) tangential to the surface

iv) at 45° to the surface

5- Magnetic induction is :-

i) scalar quantity

ii) vector quantity

iii) both

iv) none

6- Force on a moving charge in a magnetic field:-

i) q(V×B)

ii) qVB sin Ѳ

iii) both

iv) none

7- Which part of electromagnetic spectrum has largest penetrating power?

i) X- Ray’s

ii) Microwaves

iii) Gamma Ray’s

iv) visible radiation

8- Name the electromagnetic radiation used for viewing objects through haze and fog.

i) Infrared radiation

ii) visible radiation

iii) microwaves

iv) X-rays

9- A solenoid with an iron core and bulb are connected to a DC source. How does the brightness of the bulb change when the iron core is removed from the solenoid:-

i) increases

ii) decreases

iii) not affected

iv) none of the above

10- In which component of LCR circuit there is maximum power consumption:-

i) R

ii) L

iii) C

iv) none

11- Two equal point charges separated by 1m distance experience a force of 8N. What will be the force experienced by them, if they are held in water, at the same distance?(given K for water=80)

12- Why an electric dipole placed in a uniform electric field does not undergo acceleration?

13- Draw a graph to show the variation of resistance R of the metallic wire as a function of its diameter D keeping the other factors constant.

14- The difference of potential between the terminals of a cell in an open circuit was 2.2V and when it was connected through a resistance of 5 ohm, the potential difference fell to 1.8V.find the internal resistance of the cell.

15- A beam of alpha particles projected along +X axis, experiences a force due to a magnetic field along +Y axis. What is the direction of the magnetic field?

16- What are the values of horizontal component of earth and angle of dip at the magnetic north pole of the earth?

17- The voltage and current in a series AC circuit are given by V=Vo sin ωt and I=Io cos ω What is the power dissipated in the circuit?

18- Why a 220 V AC is connected to be more dangerous than 220 V DC?

19- Name the part of electromagnetic spectrum which is suitable for

i) radar system used in aircraft navigation

ii) treatment of cancer tumors.

iii) water purification

iv) eye surgery

20- Which part of electromagnetic spectrum is used in ‘RADAR’ system?

SECTION-B

21- Three charges -q, Q and -q are placed at equal distance on a straight line. If the potential energy of the system of these charges is zero, then what is the ratio Q:q?

22- A fully charged parallel plate capacitor  is connected across an uncharged identical capacitor. Show that the energy stored in the combination is less than that stored initially in the single capacitor.

23- State the principle of working of a meter bridge.

24- A non conducting ring of radius r has charge q distributed uniformly over it. What will be the equivalent current if it rotates with an angular velocity ω.

25- Define current sensitivity of a moving-coil galvanometer and write SI unit.

26- An electron passes through a region of crossed electric and magnetic fields of intensities E and B respectively. For which value of electron speed, will the beam remain undeflected?

27- Electromagnetic waves travel in a medium at a speed of 2×10⁸m/s. The relative permeability of the medium is 1. Find it’s relative permittivity.

SECTION-C

28- Find an expression for the capacitance of parallel plate capacitor having dielectric medium filled between the plates.

29- Four point charges Q,q,Q and q are placed at the corners of a square of side ‘a’ as shown in the figure.

Find:

i) resultant electric force on a charge Q.

ii) potential energy of the system.

30- Four cells of identical emf E and internal resistance r connected in series to a variable resistor. The graph shown gives the variation of terminal voltage of the combination with the current output.

i) What is the emf of each cell used?

ii) For what current from the cells, does maximum power dissipation occur in the circuit?

iii) Calculate the internal resistance of each cell.

31- Obtain an expression for the torque on a rectangular current loop when placed at angle with the direction of the magnetic field. In which condition the torque is (i) maximum (ii) minimum

32- A series L-C-R circuit is connected to an AC source having voltage V=Vo sin ω Derive an expression for the instantaneous current I and it’s phase relationship to the applied voltage. Obtain the condition for resonance to occur and show that resonant frequency is: f=1/2π√LC.

33 (i)- Determine the value of phase difference between the current and the voltage in the given L-C-R circuit.

33 (ii)-Calculate the value of the additional capacitor which may be joined suitably to the capacitor C that would make the power factor of the circuit unity.

34 (i) -Define an expression for the force between two long parallel current carrying conductors.

34 (ii)-Use this expression to define SI unit of current.

SECTION-D

35- Answer the following.

i) Explain with the help of a diagram, the principle, construction and working of a transformer.

ii) Give two causes of power loss in it. Why is it’s core laminated?

iii) Does the converting process in step-up transformer V volts, the law of conservation of energy? Explain.

iv) Write sources of energy loss in a transformer.

36- A device X is connected to an AC source V=Vo sin ω The variation of voltage, current and power in one cycle is shown in the following graph.

i) Identify the device X.

ii) Which of the curves A, B and C represent the voltage, current and the power consumed in the circuit? Justify your answer.

iii) How does it’s impedance vary with frequency of the AC source? Show graphically.

iv) Obtain an expression for the current in the circuit and it’s phase relation with AC voltage.

37- State the principle of a potentiometer. With the help of a circuit diagram, describe the method for the determination of internal resistance of a cell using a potentiometer. Derive the formula used.