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Lab Worksheet: Ohmmmmm, Ohmmmmm
Observations:
Circuit
Table 1: Lamps In Series and Parallel
Dim or Bright
Did lamp light when one bulb
was loosened?
One lamp
Bright
XXXXXXXXXXXXXXXXX
Two lamps in series
Dim
No- other went out
Two lamps in parallel
Bright
Yes – other lamp stayed lit
One battery
Table 2: Batteries In Series and Parallel
Dim or Bright
Did lamp light with one
battery disconnected?
XXXXXXXXXXXXXXXXX
Dim
Two batteries in series
Bright
No – light went out
Two batteries in parallel
Dim
Yes – lamp stayed lit
Circuit
Potential Difference
(experimental - volts)
6V
Table 3: Ohm’s Law
Current (amperes)
Resistance (ohms)
2.5
2
Potential Difference
(calculated – volts)
5.0
6V
1.2
5
6.0
6V
.6
10
6.0
12V
1.2
10
12.0
CONCLUSIONS/RELATED QUESTIONS (2 points each)
1. Compare the light given off by two lamps connected in parallel to the light produced when they are
connected in series.
Two lamps connected in parallel are brighter.
2. Why is the amount of light different when the lamps are connected in parallel?
Electricity only has to go through one lamp – less resistance.
3. What happened when you loosened one bulb in the series circuit?
Both bulbs went out.
4. Explain why this happened.
The circuit was opened and no electricity could get through.
5. What happened when you loosened one bulb in the parallel circuit?
Only that bulb went out, the other one stayed lit.
6. Explain why this happened.
There was still a complete path (through the other bulb).
7. A 9-volt battery (such as those used in radios) consists simply of six 1.5-volt batteries connected together.
Are they connected in series or parallel? (Hint: check which battery setup on the front gave more power.)
Series – bulbs were brighter in series – more “power”.
8. List one advantage of connecting batteries in series.
Brighter bulbs.
9. List one advantage of connecting batteries in parallel.
Backup battery source – bulb stayed lit.
10. List one advantage of connecting bulbs in parallel.
Only the bulb loosened went out.
11. What is the difference between an open and a closed electric circuit?
Open circuit – path is not complete, no electricity flows.
Closed circuit – path is complete, electricity flows.
12. Why should you leave the switch open while all connections in a circuit are being made?
So that you don’t risk damaging equipment or draining the battery.
13. In a series circuit, current must travel through all resistors.
14. Why are all appliances connected in parallel circuits in the home?
So that everything doesn’t turn off or on at the same time.
15. Some Christmas lights are wired in a series circuit. If one bulb burns out, all bulbs turn off.
16. From Table 3, what happens to the current as the resistance is increased?
Current decreases.
17. What happens to the potential difference when the resistance is increased?
Potential difference remains unchanged.
18. What happens to the current as the potential difference is increased?
It increases.
19. What happens to the resistance as the potential difference is increased?
It remains unchanged.
20. How do you account for the difference in the experimental and the calculated potential difference?
Friction, old resistors, ammeter not accurate, etc.
21. The relationship between current, potential difference, and resistance is called Ohm’s Law. It may be
written as:
Current = potential difference/resistance
Current may be abbreviated as I, potential difference V, and resistance R. Substituting these symbols in
the formula above gives I = V/R
Now place the symbols I, V, and R correctly in the triangle below and use this triangle to solve the
following problems.
22. Find the current when a 12 volt battery is connected through a resistance of 50 ohms.
V = 12 volts
I = V/R
I = .24 amps
R = 50 ohms
I = 12 volts/50 ohms
23. Calculate the potential difference in a circuit if the resistance is 200 ohms and the current is 10 amperes.
R = 200 ohms
V = IR
V = 2000 volts
I = 10 amperes
V = (200 ohms)(10 amperes)
24. If the current is 10 amperes and the voltage is 120 volts, what is the resistance?
I = 10 amperes
R = V/I
R = 12 ohms
V = 120 volts
R = 120 volts/10 amperes
25. What is the voltage if the current is 35 amperes and the resistance is 20 ohms?
I = 35 amperes
V = IR
V = 700 volts
R = 20 ohms
V = (35 amperes)(20 ohms)