Lesson 3.4 Homework Solutions
1.
Two resistors A and B are connected is series across a potential
difference. A has twice the resistance of B. If the current in A is 2.0
A, what is the current in B?
When the resistors are in series, the current is the same in all the
resistors. Therefore, the current in B =
2.0 A
2.
When two identical resistors are connected in series across a battery,
the power delivered by the battery is 20 W. If these resistors are
connected in parallel across the same battery, what is the power
delivered by the battery?
R
R
Total resistance = 2R
E
If E is the emf of the cell, then
the power P of the cell is:
2
2
2
Since the total resistance is 2R,
20
2
40
E
P
R
E
R
E
R
=
=
=
R
R
Total resistance = R/2
E
The total resistance when in
parallel is R/2. The power P
supplied by the battery is:
2
2
2
2
/2
4
4
20
2
80
E
E
P
R
R
R
W
E
=
=
=
⋅
=
=
×
3.
Two resistors connected in series have an equivalent resistance of 690
Ω
. When they are connected in parallel, their equivalent resistance is
150
Ω
. Find the resistance of each resistor.
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 Spring '11
 George
 Physics, Current, Resistance, Work, Resistor, Potential difference, Electrical resistance, Series and parallel circuits

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