Download Activity 2 Supplement: Ohm`s Law

Activity 2 Supplement: Ohm’s Law
Definitions
Voltage: The “push” electrons get from a battery or power supply to move through a circuit.
Units: volts (V)
Current: The flow of electrons in a circuit. Units: amps (A)
Resistance: The opposition to the flow of electrons in a circuit. Units: ohms (W)
Ohm’s law
or
voltage = current x resistance
V = IR
Series and parallel circuits
Series circuits: Rtotal =R1 + R2 + R3 + …
Parallel circuits:
Problems – Ohm’s Law
1.
Find the resistance of a vacuum cleaner that draws 9 A when connected to
a 110 V wall outlet?
2.
Find the resistance of a 120 V electric toaster that draws a current of 8
A.
3.
A 240 V water heater has a resistance of 24 W. What must be the minimum
rating (in amps) of the fuse in the circuit to which the heater is
connected?
4.
What potential difference must be applied across a 1500 W resistor in
order that the resulting current be 0.050 A?
5.
A 240 V clothes dryer draws a current of 15 A. What is its resistance?
6.
A 30 W bulb is connected to a 6V battery. What is the current?
7.
What is the resistance in a power line that carries 1200 amps of current
at a voltage of 50,000 V?
8.
At a voltage of 30 V, the current in a wire connected to a motor is 0.75
A. What is the resistance of the motor?
9.
What voltage is required to achieve a current of 0.52 A through a CD
player with a resistance of 212 W?
10. A resistance of 46,000 W connected to a 12 V power supply would
experience what current?
Problems – Series And Parallel Circuits
11. (a) A 5 W light bulb and a 10 W light bulb are connected in series. What
is the total resistance?
(b) The same bulbs are connected in parallel. What is the total
resistance now?
12. A set of holiday lights consists of 12 bulbs connected in series. Each
bulb has a resistance of 5 W. What is the resistance of the string of
lights?
13. Five 200 ohm resistors are connected in parallel. What is the total
resistance?
14. A 20 W resistor, a 40 W resistor and a 50 W resistor are connected in
parallel. Find the total resistance of the set.
15. Three 12 ohm resistors are connected in series across a 48 V power
supply. Find
(a) the total resistance,
(b) the current in the circuit.
16. Two 20 ohm resistors are connected in parallel to a 6 V battery. Find
(a) the total resistance,
(b) the total current in the circuit.
17. Resistors in parallel all “see” the full voltage of the power supply or
battery to which they are connected.
(a) What is the current in each of three 50 W light bulbs connected to a
3 V crank generator?
(b) What is the total current in all three?
18. In general, as resistors are added to a series circuit, what happens to
the total resistance?
19. In general, as resistors are added to a parallel circuit, what happens to
the total resistance?
20. Two 100 W resistors are connected in parallel, then these are connected
in series to another 100 W resistor. What is the total resistance? Hint:
Find the total for the parallel resistors first, then add this to the
series.
21. (a) Find the total resistance of a string of 50 lights, 3.5 W each.
(b) What would be the total resistance if two of these strings were
connected in parallel?
22. (a) Find the total resistance between
points a and b.
(b)Find the total resistance of the entire
circuit.
(c) Find the total current.