**Class 12 CBSE Physics Sample Question Paper for Exam 2014** - You will find here Sample Question Papers of Physics (Theory) Code A for examination 2014.

The mock test papers/sample question papers are based on previous years' question papers or dummy papers. It is needless to mention that the actual content of CBSE question papers will be completely different from the content of the Mock Test papers that appear here.

**1. **Write down the expression for electrical potential energy of system of three point charges Q1, Q2 and Q3 kept at the three vertices of an equilateral triangle of side *L*.

**2. **What do you understand by ‘‘dynamo effect’’?

**3. **About 20% of the power of a 100 W light bulb is converted to visible radiation. What is the average intensity of visible radiation at a distance 1 m from the bulb?

**4. **There are 10^{7} radioactive nuclei in a given radioactive element. Its half life is 20 s. How many nuclei will remain after 10 seconds?

**5. **A tube of hydrogen atoms in ground state is pumped with electrical energy of 12.09 eV. How many spectral lines will be detected in emission spectra?

**6. **Draw the typical input characteristics and output characteristics for a NPN transistor in CE configuration.

**7. **Refer to the base biased transistor in CE configuration below.

It is given that supply *V _{BB}* has a range of 0 V to 5 V. The Si transistor has β

_{dc}= 200 and

*R*= 150 kΩ, Rc = 1.5 kΩ. and Vcc = 4.5 V. Assume that when the transistor is saturated, VCE = 0 and VBE = 1 volt.

_{B}(a) Calculate the minimum base current, for which the transistor will reach saturation.

(b) Find Vi when transistor is switched on.

**8. **A 30 volt, 10 watt lamp is connected in series with an emf of 220 volt and frequency 50 Hz. Find the capacity of a condenser required to be connected in series with the source.

**9. **Prove that resistivity of a conductor is inversely proportional to relaxation time.

**10. **Write down the limitations of Ohm’s law.

**11. **A straight rod of length L moves on a rectangular conducting frame kept inside a uniform magnetic field B perpendicular to its length with uniform velocity v. Derive an expression for the:

(a) EMF induced in the rod.

(b) Power required to move the rod.

**12. **A 0.02 cm wide slit is illuminated at normal incidence by light having wavelength 6000 Å. What would be the width of central maximum, if the apparatus is immersed in water of refractive index 4/3 and the screen is 1 m away from the slit?

**13. **Define total internal reflection and critical angle. Find the relation between critical angle and refractive index. Under what conditions does total internal reflection take place?

**14. **A compound microscope has lenses of focal length 10 mm and 30 mm. An object placed at 1.2 cm from the first lens is seen through the second lens at 0.25 m from the eye lens. Calculate distance between the two lenses.

**15. **What is meant by interference of light? Describe briefly Young’s double slit experiment to demonstrate interference of light.

**16. **Using Gauss’s theorem derive an expression for electric field intensity at a point inside and outside a uniform spherical distribution of charge in air. Volume charge density ρ and radius R.

**17. **A plastic rod of length 4.4 m and radius 7.2 mm carries a negative charge of 7.6 × 10^{–7} C spread uniformly over its surface. What is the electric field near the mid-point of the rod, at a point on its surface?

**18. **Derive an expression for the capacitance of a parallel plate capacitor with a dielectric slab placed in between the two plates partially.

**19. **Two identical charges each of mass 10^{–2} kg and charge 200 μC each are kept 1 cm apart and released. Find the speed of each particle when they reach infinity.

**20. **A long straight solid metal wire of radius R carries a current I, uniformly distributed over its circular crosssection. Find the magnetic field at a distance r from axis of wire (i) inside and (ii) outside the wire.

**21. **Write down the principle and construction of a moving coil galvanometer.

**22. **Derive an expression for the current and voltage sensitivity of the galvanometer. Will increase in current sensitivity necessarily increase the voltage sensitivity?

**23. **Write expression for displacement current.

**24. **The potential difference across a conductor of uniform cross-section is doubled. What happens to the drift velocity of electrons inside the conductor?

**25. **The image formed by a convex mirror of focal length 30 cm is of one fourth height compared to that of the object. What is the distance of the object from the mirror?

**26. **Write the truth table of the logic gate.