THE UNIVERSITY OF BRITISH COLUMBIA
Science 1
Physics Assignment # 3:
CAPACITANCE
25 Jan. 1999 - finish by 1 Feb. 1999
- 1.
- CUBIC CAPACITOR
Suppose we take a roll of very thin
(50 m)
copper sheet and a roll of
150 m
thick strontium titanate dielectric
(dielectric constant
,
dielectric strength 8 kV/mm)
and form a capacitor as follows: cut the sheets into strips
5 cm
wide and sandwich the dielectric sheet between
two sheets of copper. Then fold the sandwich back and forth
to fill a cube
5 cm
on each side. Assuming that we can press the layers
together firmly so that there are no empty spaces, find:
- (a)
- the capacitance of the resulting cube-shaped capacitor;
- (b)
- the maximum charge it will hold without breaking down;
- (c)
- the total energy we can store in this small cube.
- 2.
- ARRAY of CAPACITORS:
The battery B supplies
6 V.
The capacitances are
C1 = 2.0 F,
C2 = 1.0 F,
C3 = 4.0 F
and C4 = 3.0 F.
(a) Find the charge on each capacitor
when switch S1 is closed but switch S2 is still open.
(b) What is the charge on each capacitor if S2 is also closed?
- 3.
- THUNDERCLOUD CAPACITOR:
A large thundercloud hovers over the city of Vancouver at a height of
2.0 km.
Between the cloud and the ground
(both of which we may treat as parallel conducting plates,
neglecting edge effects) the electric field is about
200 V/m.
The cloud has a horizontal area of
200 km2.
- (a)
- Estimate the number of Coulombs [C] of positive charge
in the cloud, assuming that the ground has the same surface density
of negative charge.
- (b)
- Estimate the number of joules [J] of energy
contained in the air between the cloud and the ground.
Jess H. Brewer
1999-01-25