Chapter 18.2 Review Capacitance and Potential

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Chapter 18.2 Review Capacitance and Potential
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1. A 5 µF capacitor is connected to a 12 volt
battery. What is the potential difference across
the plates of the capacitor when it is fully
charged?
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12 volts, a charged capacitor has the same
potential difference across the plates as the
source.
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2. What is the charge on one plate of the
capacitor in problem 1 when it is fully charged?
What is the net charge on the capacitor when it
is fully charged?
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q VCq 12 x 5 60 µCorq 12(5 x 10-6) 6
x 10-5 CBut the net charge on a capacitor is
always zero because the and plate have
charges of equal magnitude.
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3. How much electrical potential energy is stored
in the capacitor in problem 1?
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PEE ½ CV2PEE ½ 5(12)2PEE 360 µJor,PEE
½ (5x 10-6)(12)2PEE 3.6 x 10-4 J
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4. If the plates are separated by a distance of
0.003 m, what is the strength of the electric
field across the plates?
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Ed VE(0.003) 12E 4000 N/C
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5. A 9 µF capacitor is connected to a 9 volt
battery. What is the potential difference across
the plates of the capacitor when it is fully
charged?
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9 volts, a charged capacitor has the same
potential difference across the plates as the
source.
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6. What is the charge on one plate of the
capacitor in problem 5 when it is fully charged?
What is the net charge on the capacitor when it
is fully charged?
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q VCq 9 x 9 81 µCorq 9(9 x 10-6) 8.1
x 10-5 CBut the net charge on a capacitor is
always zero because the and plate have
charges of equal magnitude.
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7. How much electrical potential energy is stored
in the capacitor in problem 5?
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PEE ½ CV2PEE ½ 9(9)2PEE 364.5 µJor,PEE
½ (9 x 10-6)(9)2PEE 3.645 x 10-4 J
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8. If the plates are separated by a distance of
0.005 m, what is the strength of the electric
field across the plates?
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Ed VE(0.005) 9E 1800 N/C
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9. List four ways to increase the charge on a
capacitor.
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1. Larger plates2. Plates closer together3.
Different dielectric4. Increase voltage
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10. What is the difference in electrical
potential energy and electric potential?
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Electric potential is electric potential energy
divided by charge.
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11. A proton is moved 0.5 m in the direction of
an electric field with a strength of 5000 N/C.
What is the change in electric potential?
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Ed V5000 x 0.5 V2500 V VMoving in the
direction of the field is a decrease of
potential, so -2500 V V.
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12. What is the change in electrical potential
energy of the proton in problem 11?
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PEE qVPEE (1.6 x 10-19)(2500)PEE -4 x
10-16 J
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13. An electron is moved 0.8 m in the direction
of an electric field with a strength of 3000 N/C.
What is the change in electric potential?
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Ed V3000 x 0.8 V2400 V VMoving in the
direction of the field is a decrease of
potential, so -2400 V V.
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14. What is the change in electrical potential
energy of the electron in problem 13?
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PEE qVPEE (-1.6 x 10-19)(-2400)PEE 3.88
x 10-16 JThe electron is being moved in the
direction it does not want to go. That is an
increase in potential energy.
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15. A helium nucleus (composed of two protons and
two neutrons) is moved 24 cm in the direction of
an electric field with a strength of 9000 N/C.
What is the change in electric potential?
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Ed V9000 x 0.24 V2160 V VMoving in the
direction of the field is a decrease of
potential, so -2160 V V.
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16. What is the change in electrical potential
energy of the helium nucleus in problem 15?
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PEE qVPEE (1.6 x 10-19)(2)(-2160)(There
are two protons in one helium nucleus.)PEE
-6.912 x 10-16
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