Portal for CBSE Notes, Test Papers, Sample Papers, Tips and Tricks
CBSE Class-1 Physics Quick Revision Notes
Chapter-01: Electric Charges and Fields
•Like Charges and Unlike Charges:
Like charges repel and unlike charges attract each other.
•Conductors and Insulators:
Conductors allow movement of electric charge through them, insulators do not.
•Quantization of Electric Charge:
It means that total charge (q) of a body is always an integral multiple of a basic quantum
of charge (e)
q = ne
where n = 0, ±1, ±2, ±3, ….
•Additivity of Electric Charges:
Total charge of a system is the algebraic sum of all individual charges in the system.
•Conservation of Electric Charges:
The total charge of an isolated system remains uncharged with time.
•Superposition Principle:
It is the properties of forces with which two charges attract or repel each other are not
affected by the presence of a third (or more) additional charge(s).
•The Electric Field E at a Point due to a Charge Configuration:
It is the force on a small positive test charges q placed at the point divided by a
magnitude
2
0
| |
4
q
r
π ε
It is radially outwards from q, if q is positive and radially
inwards if q is negative.
E at a point varies inversely as the square of its distance
from Q, the plot of E versus r will look like the figure
given below.
•Coulomb’s Law:
The mutual electrostatic force between two point charges q
1
and q
2
is proportional to
the product q
1
q
2
and inversely proportional to the square of the distance r
21
separating
them.
^
12
21 21
2 1 2
21
( )
( on q due to q )k q q
Fforce r
r
=
Where
^
21
r
is a unit vector in the direction from q
1
to q
2
and
0
1
4
k
π ε
=
is the
proportionality constant.
•
An Electric Field Line:
It is a curve drawn in such a way that the tangent at each point on the curve gives the
direction of electric field at that point.
