# Very Important Long Questions Collection – All Unit | Physics Class 12

## HSEB Exam | Questions Collection Very Important Long Questions Collection For: Science | Physics Class 12 From: All Unit

We have listed some very Important Questions. The repeating frequency of this questions are Comparatively High. This questions are asked on lots of previous papers.

Disclaimer: This questions are neither guessed nor we guarantee the possibility in the coming exam. This questions are often repeated in the previous exam only.

Unit One: Wave and Optics

1. What are stationary waves? Derive an equation for such a wave. 
2. What the principle of superposition is as applied to wave motion? Discuss the result of superposing two waves of equal amplitude and same frequency travelling in opposite direction. 
3. How is a progressive wave different from a stationary wave? Derive a progressive wave equation. [2070 ‘D’]
4. What is Newton’s formula for the velocity of sound? What correction was made by Laplace? 
5. Describe the various modes of vibrations of the air column in an organ pipe. 
6. What is Doppler’s effect? Derive an expression for the apparent frequency received by a stationary observer when a source is moving away from him. 

Unit Two: Physical Optics

1. State and explain Huygens’s principle to show that a plane wave front incident obliquely on a plane mirror is reflected as a plane wave front so that the angle of incidence is equal to the angle of reflection. [2060, 2068]
2. Define Michelson’s method to determine the speed of light. Write advantages of this method over Foucault’s method. 
3. What are coherent source? Prove analytically that the bright and dark fringes in young’s double slit experiment are equally spaced. 
4. Describe Young’s double slit interference experiment to determine the wavelength of the source of light. 
5. What do you mean by polarization of light? Show that tanθp = np where θp is the angle of polarization and Ƞ is the refractive index of the transparent medium. 

Unit Three: Electricity and Magnetism

1. What do you mean by a shunt? Describe its use in converting a galvanometer into an ammeter. 
2. What is drift velocity of an electron? Derive a relation between the current through a metallic conductor and the drift velocity in terms of the number of free electrons per unit volume of the conductor. 
3. State and explain Ohm’s law. 
4. What is potentiometer? Explain how do you compare emf of two cells using potentiontiometr. 
5. What is a Wheatstone bridge? Obtain the balanced condition for the bridge. Explain how resistance can be measured by a meter bridge. 
6. Explain, what do you mean by seebeck effect? How does thermoelectric emf vary with the temperature? 
7. State and explain Faraday’s laws of electrolysis. Hence. Define Faraday’s constant. 
8. Define the formula for the magnetic field at the centre of a circular coil carrying current. Explain why the magnetic field at the centre of the coil disappears when the circular coil is made infinitely large. 
9. Derive an expression for the torque experienced by a current carrying rectangular coil placed in a uniform magnetic field and hence define magnetic dipole moment of the coil. 
10. Derive an expression of force per unit length between two parallel conductors separated by a distance ‘r’ and carrying currents I1 and I2 in the same direction. 
11. Define magnetic susceptibility and relative permeability and establish a relation between them. [2070 ‘C’]
12. Obtain the expression for the emf induced in the conductor moving in a magnetic field. 
13. State and explain Faraday’s law of electromagnetic induction. 
14. An alternating e.m.f is applied across a capacitor. Show that the current in it leads to the applied e.m.f. by 90°.

Unit Three: Modern Physics

1. Describe with necessary, theory, Millikan’s oil drop experiment to determine the value of the charge associated with an electron. [2052, 2068, 2069]
2. Describe an experiment to determine the specific charge of electron. 
3. Explain the phenomenon of discharge of electricity through gases at low pressure. 
4. Show that electron motion in magnetic field is circular. Prove that frequency and time period are independent with the velocity of electron. 
5. How are P-type and N-Type semiconductors formed? Discuss the forward biasing of a P-N junction diode. 
6. What is p-n-p transistor? Describe briefly a circuit of p-n-p transistor amplifier in its common emitted configuration. 
7. What is Zender breakdown? Describe how a Zender diode can be used as a voltage regulator? [2070 ‘C’]
8. What are X-rays? Confirm with experiment the wave nature of X-rays. 
9. What are Bohr’s postulates? Derive the formula for the radius of the third Bohr’s orbit. 
10. What are the postulates of Bohr atomic model? Obtain an expression for the energy of nth orbit of hydrogen atom. 
11. State and explain Einstein’s mass energy relation with example. 
12. Discuss fission and fusion with an example of each. In which reaction is the energy released greater? [2070 ‘C’]
13. Explain the term “artificial radio-isotopes”. [2054, 2054]
14. Discuss energy crisis in a modern society. 
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