Download current = potential difference resistance •1. Find the unknown

current
=
potential difference
resistance
I
=
V
R
Units: R is C (ohms)
V is V (volts)
I is A (amperes)
•1. Find the unknown quantity:
a)
l=1OA
R=15OOC
V=?
b) 1?
R=200C)
V=240V
c) l=15A
R=?
V=1IOV
2. Find the unknown quantity (Don’t forget to convert units)
a) 1?
R=20001)
V=2OmV=
‘________
[b) l25mA
R=?
V=11OV
A
c) l=lkA=
R=?
V=5OmV=
A
_
3. How much resistance does a light bulb create if it has a current of 25 mA through it in a 9 V
circuit?
4. A heating coil offers a resistance of 2.5 kO. What voltage is required so that 1.5 A of current
pass through it?
5. The human body offers a very small amount of resistance (let’s say I mC2 for argument). If a
lightning bolt (said to have 1.21 GV of potential according to a famous movie called Back to the
Future released in 1984), hits you how much current is flowing through your body.
.
T
I
Resistors in parallel
J
V
1’
Sit1
Requivatent = R
1
/
Requjvaient
1
R
+
4 R
2
R
3=
2
R
3
R
6. Find the equivalent resistance of these series circuits (in f2):
a) 1
R = 100 2
=20
2
R
55C)
3
R
1J7.
1 = 0.1 C2
R
[ c) R
=O.20
2
b) 1
R = 7500 fl
=1.5kC
2
R
25Q
3
R
I
R
=
3
5Omfl
Find the equivalent resistance of these parallel circuits (in 0):
a) 1
R = 100 0
=200
2
R
=550
3
R
b) 1
R = 7500 0
=1.5k0
2
R
=250
3
R
c) 1
R = 0.1 0
=O.20
2
R
=50m0
3
R
8. The same two equations above work for any number of resistors in a circuit. If a fourth resistor
is added (R
4 85 0), find the equivalent resistance in 5a) and 6a).
6a)
7a)
V
.
1
9. Calculate the equivalent resistance of the following circuits:
.
aR=5C R
= 100
2
H
12
b) R
1
=
I
T
=
3
R
1.5 0
=
(
..i
i
c) R
= 120 2
1
R
=
50 3
R
=
8
I
L____
1
\
d) R
1
=
I 0 2
R
=
20 3
R
=
30
R
=
4
40
10. Three light bulbs of 4 0 resistance each are in a parallel with a 9V power supply. Draw the
circuit, and find the current through the circuit.
11. Three identical buzzers are in parallel with a 110 V power supply. The circuit has a current of
1.5 A. Draw the circuit. Find the resistance of one buzzer.
12. Find the resistance of the light bulb in this circuit. The cell is 1.5 V, and the ammeter is
reading 85 mA.
.I/
13. (a) Draw a circuit that has two light bulbs connected in series with a 9 V battery and an
ammeter. (b) If the same light bulbs as in the last problem are used, what is the current on the
ammeter? (Hint: because there are two light bulbs there is twice as much resistance)
14. The school’s fire alarm consists of a circuit that has a 150 0 buzzer, and a 100 0 blinking light
connected in series with a 110 V power source, and a switch (closed when someone pulls the fire
alarm)
(a) Draw this circuit (b) Find the current that flows through this circuit when someone
•
pulls the alarm.
15. (a) Draw a circuit with a 10 kO resistor, a cell(battery), an ammeter, and a switch all in series.
(b) If the ammeter reads 155 mA what is the potential difference across the cell (battery).
.