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# Electricity and Magnetism

1. What is the electric field strength E at a point 0.400 m from a point of charge of + 1.75 microC?

a. 2.00 x 10^5 N/C
b. 9.85 x 10^4 N/C
c. 1.21 x 10^5 N/C
d. 8.91 x 10^5 N/C

2. What is the Electric potential at a point 0.90 m away from a point charge of 2.5 mC?

a. 10 MV
b. 25 MV
c. 35 MV
d. 5.0 MV

3. A flashlight lamp connected to battery that provides 2.8 V draws a current of 0.10 A. What electric power is used by the lamp?

a. 0.28 W
b. 14 W
c. .077 W
d. 140 W

4. A 100 ohm resistor is joined in parallel with a 0 ohm resistor. What is the equivalent resistance?

a. 32 ohm
b. 147 ohm
c. 50 ohm
d. 0 ohm

5. A wire 0.250 m long carries a current of 0.750 A in a region of uniform magnetic field. The wire is subject to a force of 5.00 N when held perpendicular to the direction of the field. What is the magnitude of the magnetic field?

a. 11.1 T
b. 1.21 T
c. 26.6 T
d. 1.97 T

6. A transformer is made by winding a primary coil of 250 turns around an iron core. A secondary winding of 50 turns is made around the same core. If the primary voltage is 240 V, what is output voltage on the secondary?

a. 24 V
b. 12 V
c. 48 V
d. 120 V

#### Solution Preview

1. What is the electric field strength E at a point 0.400 m from a point of charge of + 1.75 microC?

a. 2.00 x 10^5 N/C
b. 9.85 x 10^4 N/C
c. 1.21 x 10^5 N/C
d. 8.91 x 10^5 N/C

Answer: b. 9.85 x 10^4 N/C

E = Q/(4 pi epsilon o r^2 )
Q= 1.75E-06 C
r= 0.400 m
1/(4 pi epsilon o)= 9.00E+09 N-m^2/C^2

Therefore E= 9.84E+04 N/C

2. What is the lectric potential at a point 0.90 m away from a point charge of 2.5 mC?

a. 10 MV
b. 25 MV
c. 35 MV
d. 5.0 MV