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Magnets & Current

Test XXI , XVII, XVIII, XIX


I. Matching (2%)

___1. Opposing sides of a magnet that are attracted to the North and South of the Earth.

___2. A magnet formed by temporarily surrounding an iron core in a magnetic field.

___3. The ability of a device to build up a charge and let it flow only when it reaches some predetermined level.

___4. Electricity created by batteries is ....

___5. An analogy that helps to visualize the direction of electron flow and magnetic fields.

___6. Electricity that goes back and forth, constantly changing.

___7. The strength of electrical energy, created because 2 points have different charges.

___8. The rate of flow of electricity.

___9. The tendency of a substance to limit the flow of electricity. Freq power

II. Matching – Match units concepts. (2%) A. Watt B. Hertz C. Ohm D. Ampere E. Volt F. Farad

___1. Power ___2. Capacitance ___3. Potential Difference ___4. Resistance ___5. Electrical Power ___6. Current ___7. Frequency


III. Label 4 parts of the circuit. Tell what they represent in electrical terms. (2%)


IV. Problems – show ALL work and put an answer in the blank to the left of each. (0% or 5%)

_____________1. A resistance of 50W allows a current of 800mA to pass through it when it is connected to the terminals of a battery. What is the voltage of the battery?




_____________2. If a current of 1500mA flows through the headlight of a car running on a 12V battery, how much power does it take to run the light?


_____________3. Kuuurraashshsh, Kapow! If that lightning bolt put out 20kV of electricity, and the bolt only carried 0.5A of current, what was the resistance of the air today?



_____________4. I have a simple circuit consisting of a 9V battery with a 2.5W resistor connected across its terminals. How much current does it use?




_____________5. What is the Resistance of a typical 60W bulb at your house?





_____________6. Bob bought a roll of wire labeled “520mW/meter”. If he uses 350cm of it to connect a new amplifier in his trunk, how much resistance does the wire add to the circuit?




_____________7. If Bob's car has a typical 12V battery, how much power does that new wire use up?





VI. On a separate page, finish the following thoughts. Be thorough. (5%) A. Similar charges ... ... ..., but if the charges are different ... ... , so, when we dropped little pieces of paper on the Van deGraaff generator... ... . B. If you increase the resistance ... ... ..., but if you lower the resistance ... ... .

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