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Daily Archives: June 21, 2011

Free electrons in Materials and shock?!

Sachin asks: “Sir I am not able to understand that conductors n insulators have free electron n moving randomly in direction but the definition says that FLOW OF CHARGE PER UNIT TIME IS CALLED CURRENT. SO my question is electrons are moving in both conductors or insulators but when touch them they don’t produce electric current why ???”

Image formed by a thick Plane Mirror

“A thick plane mirror forms a number of images of a point source of light . which image is brightest ?”

Answer: In the case of a thick plane mirror, reflection takes place at the two surfaces, (top and bottom surfaces) and images are formed due to both. The second surface is silvered and therefore the second image is the brightest. Further images are formed due to multiple reflections and due to absorption of light by medium the images become fainter.

If the front surface of the mirror is silvered, only one image will be formed.

A few Questions from electricity, em waves, kinematics

Riya Posted:

1) A particle moves along a straight line parallel to the x-axis at a constant velocity, Its angular momentum about the origin?

2) Can a free electron moves from higher potential to low potential?

3) Progressive wave carries energy in a plane perpendicular to the plane wave front-is the statement true?

4) Why a heavier body doesn’t fall more quickly than a lighter body?

5) Is it possible to transfer electic charge from a body of a lower potential to a higher potential?

A Problem from Projectile motion

“A ball  is projected vertically  upwards  with  an initial  velocity of 28m/s and is observed  to pass a  point  30m above  the  projection point,at what  2times does  the ball  pass these  points?”

ans : 1.356 sec and 1.444 sec .
sol:
from v=u+at we get t=2.8 . (time taken to reach the max height )
fm v2-u2=2aS we get S=39.2 m (max height reached)
observer at 30 m .
so , in btw distance btw observer and ball (at the top) =9.2 m
at top ball is at rest and time taken to reach the observer can be calculaed from S=ut + 1/2 at2 ,we get t=1.356s .
and next time can be calculated by 2.8 – 1.356 =1.444 sec .

(The answer has not been scrutinized. If any error, teachers and visitors can post as comment)

Screw Gauge

Neeraja asks: “in screw guage the nut is a fixed one or not?”