DWARKA INTERNATIONAL SCHOOL SECTOR-12, DWARKA, NEW DELHI-78 PHYSICS(Sample paper) HALF YEARLY EXAMINATION MAX MARKS: 50 Class -XII TIME: 3 hours

GENERAL INSTRUCTIONS: 1. All questions are compulsory.

2. Question numbers 1-5 are 1 mark questions.

3. Question numbers 5-10 are 2 marks questions.

4. Question numbers 11-22 are 3 marks questions.

5. Question number 23 is a VBQ and carries 4 marks.

6. Question numbers 24 and 26 are 5 mark questions.

1. Force between two point charges kept at a distance d apart in air is F. if these charges are kept at the same distance in water, how does the electric force between them change?

2. If potential difference V applied across a conductor is increased to 2V, how will the drift velocity of the electron change?

3. State two properties of the material of the wire used for suspension of the coil in a moving coil galvanometer?

4. Why core of the transformers are laminated.

5. Draw a graph to show the variation of inductive reactance with frequency.

6. An A.C source of rms voltage V is put across a series combination of an inductor L,

capacitor C and a resistor R. if VL, VC and VR are the rms voltage across L,C and R

respectively then why is V VL + VC + VR? Write correct relationship among VL, VC and

VR.

7. The circuit shown here uses an airfield parallel plate capacitor. A dielectric is introduced between the plates of the capacitor. Explain with reason the effect on the brightness of the bulb B. 8. Write the expression for the force acting on a charged particle of charge q moving with velocity is in the presence of magnetic field B. Show that in the presence of this force. (a) The K.E. of the particle does not change. (b) Its instantaneous power is zero. 9. V.I graph for a metallic wire a two different temperatures T1 and T2 is shown in figure. Which of these two temperatures is higher and why?

10. Given a uniform electric field = 5 x 103 N/C, find the flux of this field through a square of l0 cm on a side whose plane is parallel to the y-z plane. What would be the flux through the same square if the plane makes a 300 angle with the x-axis? 11. State the underlying principle of a cyclotron. Write briefly how this machine is used to accelerate charged particles to high energies.

12.

13. Obtain the expression for the energy stored per unit volume in a charged parallel plate capaci 14. 15. In the network shown in the figure, use Kirchhoff’s rules to calculate the power consumed by resistance R= 4 Ω. 16. Two parallel plate capacitors

of capacitances C1 and C2 such that C1= are connected across a battery of V volts as shown in the figure. Initially the key (k) is kept closed to fully charge the capacitors. The key is now thrown open and a dielectric slab of dielectric constant ―K is inserted in the two capacitors to completely fill the gap between the plates. Find the ratio of (i) the net capacitance and (ii) the energies stored in the combination, before and after the introduction of the dielectric slab.

17. Consider the motion of a charged particle of mass m and charge q

18. Define the average power of an ac current. Show that the average power of ac over a complete cycle is zero. 19. Define eddy currents. Explain how they are used to stop the fast moving trains. 20. A galvanometer with a coil of resistance 120Ω shows a full scale deflection for a current of 1 mA. Calculate the value of resistance required to convert it into (a) an ammeter of range 0 to .5 A and (b) a voltmeter of range 0 to 3 V. Draw the diagrams to show how you will connect this resistance to the galvanometer in each case. 21. Compare the diamagnetic, paramagnetic and ferromagnetic substances in terms of their, permeability, susceptibility by giving one example of each type of material.

22. The potentiometer circuit shown, the balance (null) point is at X. State with reason, where the balance point will be shifted when

23. Geetika got selected for MBBS course. Her mother was packing the stuff’s, Geetika would need in the hostel. Her mother told Geetika that we should go to the market, to an electric heater, which would be useful for heating the food or making tea in case she wants to have while studying, late night. Geetika convinced her mother to purchase an induction stove, in place of electric heater and finally her mother got convinced.

a) What are qualities you find in Geetika?

b) If Geetika purchased an induction stove of 8 H inductor and the current changes form 10 A to 7.5 A in 0.08 sec. calculate the emf generated.

24. 25. A) Define electric flux. Write its S.I units.

b) Using Guass’s law, find the electric field due to uniformly charged hollow sphere at a point (i) outside the sphere (ii) on the surface of the sphere (iii) inside the sphere.

26. A) Write any two points of differences between Emf and potential difference.

B) Why can’t we use a voltmeter to find the emf of a given cell.

C) Using a schematic diagram explain how potentiometer is used to find the emf of a given primary cell.