Scientific Instruements

 

Q Why temperature less than absolute zero is not possible?

 

Ans.     According to the kinetic interpretation of temperature, absolute temperature means the  kinetic energy of molecules. As heat is taken out,    the temperature falls and hence velocity decreases. At absolute zero, the velocity of the    molecules becomes zero i.e. kinetic energy   becomes zero. So no more decrease in K.E. is  possible, hence temperature cannot fall further.

Dimensional formulae Different Physical quantities +2 physics

 

Q. Derive an expression for electric field intensity due to a point charge.

 

Which Material Cannot be Used to Make a Lens?

1.  Glass and water are transparent materials. There is a certain amount of plastic that is transparent so that the plastic can be used to make any Lens, but the clay is an opaque substance so that the light cannot be transmitted into it but clay cannot be used to create the Lens. One of the most common ways of creating a Lens is also by using the optical glass but then to make Lens generally crystals and plastics are also utilized and also mirrors are generally constructed out of any which can be polished or reflected.

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The energy of a charged particle moving in a uniform magnetic field does not change. Why?

The force on a charged particle in a uniform magnetic field always acts in a direction

perpendicular to the motion of the charge. Since work done by the magnetic field on the

charge is zero, hence energy of the charged particle will not change.

Corona discharge

• When an uncharged body is brought near a charged body having sharp corners there is large number of charges at the corners. Due to induction, they induce large number of opposite charges. This creates a very strong Electric field between them. Finally the dielectric strength breaks-down and there is fast flow of charges. This Spray of charges by spiked object is called Corona discharge. 
• The lightening arrester work on the principles of Corona discharge where the charge pass through conductor of arrester, and the buildings are saved 

The working of a rocket is based on the principle of

 (a) Elasticity 

(b) Kepler's law  

(c) Newton's law of gravitation 

(d) Conservation of momentum.

THE RIGHT ANSWER IS

(d) Conservation of momentum.

REFRACTION OF LIGHT

 

Change in momentum is given by

(a) Force x Mass 

(b) Force x Time 

(c) Force x Velocity 

(d) Force x Distance. 

THE RIGHT ANSWER IS

(b) Force x Time 

The units of Impulse are same as that of

 

(a) Energy 

(b) Linear momentum 

(c) Velocity 

(d) Power. 

RIGHT ANSWER IS 

(b) Linear momentum 

Rules for writing units

1) The symbol of a unit, which is not named after a person, is written in lower letter (small letter). 

Eg: metre (m) kilogram (kg) 

2) The symbol of a unit, which is named after a person, is written with a capital initial letter. 

Eg: newton (N), kelvin (K) 

3) Full name of a unit, even if it is named after a person is written with a lower initial letter. 

Eg: newton, kelvin. 

4) A compound unit formed by multiplication of two or more units is written after putting a dot or leaving a space between the two symbols.

Eg: newton metre — N.m or N m. 

5) A unit in its short form is never written in plural. 

The magnetic field of earth is due to:

 

      (A) induction effect of the sun
      (B) the presence of a large magnet at the centre of  the earth
      (C) interaction of cosmic rays with the current of earth
      (D) motion and distribution of some material in an outside the earth

Correct Answer is

Option (D)