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# Resistance and Ohm's Law (Grades 11-12)

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## Resistance and Ohm's Law

Instructions: Read each question carefully. Choose the answer that best fits the question. If the question involves calculations, you must show all your math work.

1.
Brooke was watching T.V., charging her iPod, heating up her curling iron, and blow-drying her hair. When she plugged in her super-deluxe Austin Mahone singing make-up mirror with extra bright halogen bulbs the power went out and she caught a faint scent of burning rubber. What best explains what happened?
1. Each device she added to the series circuit increased the total resistance. The voltage had to increase to provide current until it became so high it had to shut down.
2. Every device she plugged in acted as a new resistor on a parallel circuit. This increased the resistance to the point that there was not enough voltage to power all the devices.
3. Every device she plugged in acted as a new resistor on a parallel circuit. This would decrease the overall resistance on the parallel circuit and therefore increase the current flowing in the wires. Increasing the current generates more heat in the wire, causing a switch called a "circuit breaker" to open, stopping the flow of current in an attempt to prevent fire.
4. Wizards obviously.
2.
You invent a device that requires a minimum of 5 amps to operate, but can only handle a maximum of 8 amps without being destroyed. Assuming that it will be plugged into an outlet in the U.S. which has a voltage between 110 Volts and 120 Volts, what range of resistance can your object have to work safely?
1. Between 15 Ohms and 22 Ohms
2. Between 13.75 and 24 Ohms
3. Between 30 and 40 Ohms
4. None of the above
3.
What is the relationship explained by Ohm's Law?

4.
A resistor and voltage source are connected in a simple closed circuit, as shown here. The resistor obeys Ohm’s law.
A.
If the voltage, V, doubles but resistance stays the same, what happens to the current I? Explain your answer.

B.
If the resistance, R, doubles but the voltage remains unchanged, what happens to the current? Explain your answer.

5.
Two simple closed circuits are constructed. Circuit A has a 6V battery and a resistor on the wire drawing $24 Omega$. Circuit B has the same voltage with a current of $0.3A$. If you compare the two circuits, which statement is correct about the amount of current?
1. A carries a larger current than B.
2. A carries a smaller current than B.
3. A and B carry equal amounts of current.
6.
A resistor with $R=101Omega$ is connected across a 1.50 V battery. How much current flows through the resistor?

7.
Because of advances in lighting technology research, a halogen incandescent light bulb needs only 43 watts to produce the same amount of light as an "old-fashioned" 60-watt incandescent bulb. Both have a tungsten filament. How much more efficient is 43W halogen incandescent bulb, why is it able to last longer the 60W regular incandescent bulb, and how do you know what to buy to replace your old bulbs?

8.
Explain the relationship described by Ohm's Law in terms of mathematical proportionalities.

9.
If you connect three identical resistors in series and in parallel, in which case will they have a smaller equivalent resistance and why?

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