# CBSE SAMPLE PAPERS, Physics

# CLASS XII

# Current Electricity

**ONE MARK EACH**

- Name a physical quantity whose unit is v-m, C-m
- Equipotential surfaces are perpendicular to each other. Why?
- A 100watt bulb and 50 Watt are joined in series and connected to the main which bulb will blow bright?
- What happens to the drift when velocity V
_{d}of the electrons and to the resistance are if the length of the conductor is doubled keeping PD unchanged. - What is the effect of temperature on the conductivity of an electrolyte?

** **

**TWO MARK EACH**

** **5 Two wires of the material have same length but their cross sections are in ratio

3:1 .they are joined series the resistance of shorter wire is 10 ohm calculate the

total resistance of the combination?

6 A Copper wire is starched to make it 0.2%larger, what is the %change in resistance?

7 A wire with a circular cross section of radius 0.15mm blows at 15 amp. What should be the area of cross section of a fuse wire made of the same material which will blow at 30 amp.

8 A proton placed in an electric field of magnitude 2000N/C moves between 2 points in the direction of electric field. If the distance plates is 0.2m Find the value a) Potential difference between the points b) Work done

9 2 points electric charges of unknown magnitude and sign are placed at a distance d apart the electric field intensity is zero at a point not between the charges but on the line joining them write essential conditions for this to happen

10 Using Gauss law, show that no electric field intensity exists inside a hollow charged conductor.

11 Explain why the capacity of a parallel plate capacitor increases when a dielectric slab is introduced between the plates?

12 State Faradays law of electrolysis Derive a relation connecting chemical equivalent and electro chemical equivalent.

13 Define See beck effect. Mention 2 factors on which a)neutral temperature and b)temperature of inversion depends

**THREE MARK EACH**

14 Show that the force on each plate of a parallel plate capacitor has c magnitude =1/2QE where Q is the charge on the capacitor and E is the magnitude of electric field between the plates .Explain the origin of the factor 1/2 .

15 It is decided to deposit 0.54 kg of silver /hour on the cathode of a silver nitrate where resistance is 0.72m ohm. How much PD must be maintained between the electrodes (relative atomic mass of silver =108)

16 Define the term conductivity of metallic conductor. Show that conductivity of metals decreases with temperature.

17 With the help of a circuit diagram explain how will you compare the emf ’s of the primary cells using a potentiometer ?

18 Define the term drift velocity. Derive a relation between drift velocity and current.

19 A Particle of mass ‘m’ and charge ‘q’ is released from rest in a uniform electric field of strength ‘E’ .Describe its motion and find the distance traveled and kinetic energy acquired by it in time ‘t’

20 Show that there is always a loss of energy when two charged conductors at different potentials are connected together.

21 A storage battery of emf 8V and internal resistance 0.5 ohm is being charged by a 120 V dc supply using a series resistor of 15.5 ohm. What is the terminal voltage of the battery during charging? What is the purpose of having series resistor in the charging circuit?

22 Define the drift velocity and relaxation time. Obtain a relation between them?

23 Two cells of emf 3V and 4v of internal resistances 1ohm and 2 ohm are connected in parallel so as to send current in the same direction through an external resistance of 5 ohm. Calculate the current through each branch.

** **

**FIVE MARK FOR EACH **

24 Show by graph ‘Q’ given to a capacitor varies with its potential difference. Using the graph prove that the energy of a capacitor is 1/2 CV²

OR

Is a electric field intensity zero at point where electric potential is zero. Illustrate your answer. Derive an expression for electric potential at a point on the axial line of an electric dipole.

26 State Krichoff’s law of an electrical circuit. Derive the condition for balance in a Wheatston’s bridge.

OR

Define the terms resistivity of a metallic conductor. Give its unit. With the help of circuit diagram, how will you compare the resistance of two resistors usingMeterBridge?

27 State Gauss’ theorem. Give its mathematical form. Use it to derive an expression for electric field intensity at a point due to an infinitely long straight line of charge.

Show diagrammatically the orientation of the dipole in an electric field for which torque in (1) maximum (2) half the maximum value. Derive an expression for electric field intensity at a point on the axial line of an electric dipole.

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