Page 79 - Physics 10_Float

ELECTROSTATICS

50 volts, find the quantity of charge stored on each plate. Physics insight
Solution: Given that; V = 50 V, C = 100 F = 100 × 10 F µ -6 A voltage across a device, such
Using the formula as capacitor, has the same
Q = C V meaning as the potential
Putting the values difference across the device.
-6
Q = 100 × 10 F × 50 V For instance, if we suppose
that the voltage across a
-3
= 5 × 10 C = 5 mC capacitor is 12 V, it also means
Charge on each plate will be 5 mC, because each plate has that the potential difference
equal amount of charge. between its plates is 12 V.

Combinations of Capacitors For your information
Farad is a bigger unit of
Capacitors are manufactured with different standard capacitance. We generally use
capacitances, and by combining them in series or in parallel, the following submultiples:
-6
1 micro farad = 1 μF = 1 × 10 F
we can get any desired value of the capacitance.
-9
1 nano farad = 1 nF = 1 × 10 F
(i) Capacitors in Parallel -12
1 pico farad = 1 pF = 1 × 10 F
In this combination, the left plate of each capacitor is
+ -
connected to the positive terminal of the battery by a c 1 Q 1
conducting wire. In the same way, the right plate of each
capacitor is connected to the negative terminal of the battery + - Q 2
(Fig. 13.14). c
2
This type of combination has the following characteristics: + -
1. Each capacitor connected to a battery of voltage V c Q
has the same potential difference V across it. i.e., 3 3
V = V = V = V
2
3
1
2. The charge developed across the plates of each + –
capacitor will be different due to different value of K V
Fig.13.14: Capacitors in
capacitances .
parallel combination
3. The total charge Q supplied by the battery is divided
among the various capacitors. Hence,
Q = Q + Q + Q For your information
1 2 3 Three factors affect the ability
Q = C + V C V + C V
1 2 3 of a capacitor to store charge.
or Q 1. Area of the plates
V = C + + C 2 C 3 2. Distance between the
1
or plates
3. Type of insulator used
4. Thus, we can replace the parallel combination of
between the plates.
capacitors with one equivalent capacitor having
capacitance C , such that
C eq eq = C + + C 2 C 3
1

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