Class 12 physics Model Questions

 Class 12 physics Model Questions

                                           NEB GRADE XII 

2075

PHYSICS 

                                                Time - 3 hours

Group A

1. answer in brief , any four

a. why do we prefer a potentiometer with longer wire ?

b. Why is lead used as a standard reference metal in thermo - electricity ?

c. Why is the conductivity of an electrolyte is low in comparison  to that of metal ?

d. A solenoid tends to contract when a current flows through it.Why ?

e. What is the significance of the area of hysteresis loop ?

f. Birds siting on a high tension line wire fly off when current is awitched on.Why?

2. Answer in brief, any four questions

a.  Why is a magnetic field used to deflect electron beam but not an electric field in a T.V. picture beam ?

b. In a transistor , emmiter - base junction is always forward biased.Why ?

c. Define acid rain and write it's adverse effect.

d. All nuclei have nearly the same density , Why ?

e. Distinguish between leptones and quarks .

f. Give two evidence to show that the universe is expanding.

3. Answer,in brief,any one question

a. Frequency is the most fundamental property of wave.Why ?

b. Why is the voice of woman more intelligible than that of man ?

4. Answer,in brief , any one question

a. Distinguish between wavelet and wavefront.

b. Can ultrasonic wave can be polarized ?

Group B

5. Answer any three questions 

a. State and explain Joule's law of heating.Deduce and expression for heat developed in a conductor due to the passage of an electric current.

b. State Kirchhoffs law and use them to derive Wheatstone's bridge principle.

c. State Ampere's law and use it to find magnetic field due to a long straight current carrying conductor and toroid .

d. derive expression for the impedence of an ac circuit containing a resister an inductor and a capacitor . Hemce derive  resonance frequency . also,draw the phase diagram. 

6. Answer any three questions

a. Describe the theory of the Milikan's oil drop experiment of determine the charge of an electron.

b. What are the avalanche effect and zener effect ? How can a zener diode be used as voltage regulator ?

c. Describe Coolidge tube for the production of the X - rays . How do you control  i. the intensity ii. the penetrating power of the emitted X - rays ?

d. State the law of radioactive disintegration . Derive the relation between half life and decay constant .

7. Answer any one question

a. Describe Michelson's method for determining the speed of light .

b. Explain Fraunhoffer diffraction at single slit.

  8. Answer any one question

a. What are harmonics ? Explain the formations of the overtones in an open organ pipe and a closed organ pipe.

b. What is Doppler's effect ? Obtain an expression for the apparent frequency heard by a listener due to a source when both are approaching each other .

Group C

10. Answer any two numerical questions.

a. Two resistances of 1000 ohm are placed in series with 50 volt main supply.What will be the reading on a voltmeter of internal resistance 2000 ohm when placed across the 1000 ohm resister ? What fractional change in voltage occurs when voltmeter is connected ?

b. A horizontal straight wire 5 cm long weighing 1.2 per gm is placed perpendicular to a uniform horizontal magnetic field of flux density of 0.6 T . If the resistance per unit length of the wire is 3.8 ohm per m , calculate the p.d that has to be applied between the ends of the wire to make it just self - supporting.

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