8
Electricity
1. Determine the magnitude and direction of the electric force on the
electron of a hydrogen atom exerted by the single proton (Q2 = +e)
that is the atom’s nucleus. Assume the average distance between the
revolving electron and the proton is r = 0.53 x 10-10 m.
UNIT 8 VOCAB
Coulomb’s Law
Conduction
Induction
Electric potential
Voltage
2.
Two positive point charges, Q1 = 50uC and Q2 = 1uC are separated by
the distance l. Which is larger in magnitude, the force that Q1 exerts
on Q2, or the force that Q2 exerts on Q1?
Current
Ground
Ohm’s Law
Resistor
Resistivity
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3.
Three charged particles are arranged in a line, as shown. Calculate the net electrostatic force on
particle 3 due to the other two charges.
4. Calculate the net electrostatic force on charge Q3 due to the charges Q1 and Q2.
5. Where could you place a fourth charge Q4 = -50uC, so that the net force on Q3 would be zero?
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6. (17-1) Suppose a negative charge, such as an electron, is placed near the negative plate at point b, as
shown. If the electron is free to move, will its electric potential energy increase or decrease? How will
the electric potential change?
7. (18-1) A steady current of 2.5 A exists in a wire for 4.0 min.
a. How much total charge passes by a given point in the circuit during those 4.0 min?
b. How many electrons would this be?
8.
What is wrong with each of the schemes shown in the figures for lighting a flashlight bulb with a
flashlight battery and a single wire? EXPLAIN
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9.
A small flashlight bulb draws 300mA from its 1.5 V battery.
a. What is the resistance of the bulb?
b. If the battery becomes weak and the voltage drops to 1.2 V, how would the current change?
10. Current I enters a resistor R as shown.
a. Is the potential higher at point A or at point B?
b. Is the current greater at point A or at point B?
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11. A 65.0 ohm resistor is connected to the
terminals of a battery whose emf is 12.0 V
and whose internal resistance is 0.5 ohms.
Calculate a) the current in the circuit, b) the
terminal voltage of the battery.
IMPORTANT EQUATIONS AND UNITS
COULOMB’S LAW
OHM’S LAW
AMPS
WATTS
VOLTS
12. The lightbulbs in the figure are identical. Which configuration produces more light? Which way do you
think the headlights of a car are wired?
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13. Two 100 ohm resistors are connect in a) parallel and b) in series to a 24.0 battery. What is the current
through each resistor and what is the equivalent resistance of each circuit?
14. How much current is drawn from the battery shown in the figure?
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15. What is the current I through the 500 ohm resistor in the figure?
16. The circuit in the figure has three identical lightbulbs, each of resistance R. a) When switch S is closed,
how will the brightness of bulbs A and B compare with that of bulb C? b) What happens when switch S is
opened?
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17. A 9.0 V battery whose internal resistance r is 0.50 ohms is connected in the circuit shown.
A) How much current is drawn from the battery?
B) What is the terminal voltage of the battery?
C) What is the current in the 6.0 ohm resistor?
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18. Calculate the currents I1, I2, and I3 in the three branches of the circuit below.
1.
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