important question of physics class 12th

Question 1:

  An electron beam projected along + X-axis, experiences a force due to a         magnetic field along the y-axis. The direction of the magnetic field 

  ans: +z-axis

Question 2:

Faraday s laws are consequence of the conservation of

ans: energy

Question 3:

 An e.m.f. of 16 volts is induced in a coil of inductance 4H. The rate of change of current must be

ans: 4A/S

Question 4:

A coil with negligible resistance has 50V across it with 10 mA. The inductive reactance is

And:5000 Ohm

Question 5:

In a pure capacitive circuit if the frequency of ac source is doubled, then its capacitive reactance will be

ans: halved

Question 6:

In which of the following circuits the maximum power dissipation is observed ?

ans: pure resistive circuit

Question 7:

 A Semiconductor has temperature coefficient of resistance.

ans: positive 

Question 8:

when a pure semiconductor s heated, its resistance.

ans: Decrease(goes down)

Question 9:

A cell is connected across two points A and C of a uniform circular conductor as
shown in the figure given below. What is the value of magnetic field at the centre of the circular conductor? (given radius of conductor is

ans : 0

Question 10:

The S.l unit of Pole strength is-

ans: AM

Question 11:

The law that the induced e.m.f. and current always oppose the cause producing them

ans: LenZ

Question 12:

A heating element 5 marked 210V, 650 W. The value ot the current drawn by the
element when connected to a 210 V dc source 15.

ans:

$P=VI$, 

$\frac{P}{V}=\frac{630}{210}=3A$      

$\frac{V}{I}=\frac{210}{3}=70\Omega$

Question 13:

50 cm long solenoid has a radius of 1 cm and is made up of S00 turns. fit carries a
current of 5 A then, the magnitude of magnetic field inside the solenoid is -

Question 14:

 The semiconductor device that can be used to regulate an unregulated DC power
 supply is

ans: To regulate an irregulated dc power supply, the semiconductor device used is zener                   diode as voltage regulator. For its I-V characteristics and working,

Question 15:

 The force per unit length between two parallel long current carrying conductor is F. the current in each conductor is tripled, what would be the value of the force per unit length between them?

Question 16:

 What is the angle of dip at a place where vertical and horizontal component of earth's field are equal?

ans:  45 degree

Question 17:

At what temperature would an intrinsic semiconductor behave like a perfect insulator?

ans:  an intrinsic semiconductor behaves as a perfect insulator at temperature 0k