Download PHYSICS 7

PHYSICS 7
PRACTICE MIDTERM EXAM (Ch. 15 – 21)
1. Three electrically charged particles are positioned at the corners of a right
triangle, as shown below. The particles have the following charges: q1 = +4.81
C, q2 = +3.42 C, q3 = -5.05 C. Calculate the magnitude and direction of
net force on q2.
k = 8.99 X 109 N-m2/C2. (One C is one microCoulomb = 1X 10 –6 C)
Ans: 0.0175 N at  = 34.8 degrees clockwise from +x
2. Calculate the electric potential at position P, shown below, due to the charges
q1 and q2, where q1 = 4.81 microCoulomb and q3 = -5.05 C.
k = 8.99 X 109 N-m2/C2
Ans: . 1950 Volts
3. Each plate of a parallel-plate capacitor has an area of 0.0059 m2. The plate
separation is 2.30 mm and the space between the plates is filled with an oil
whose dielectric constant is  = 47.3. How many volts are required to place
71.4 C of charge on this capacitor? o = 8.85 X 10-12 C2/N-m2.
Ans: 66,500 volts
4. (5 pts) Three 15-ohm resistors are placed in a circuit as s shown below.
Calculate the equivalent resistance of the resistors in the circuit.
Ans: 5 
5. Calculate the voltage drop across the 5.0-ohm resistor shown below.
Ans: 5.0 volts
6. Suppose a 14.2-mT (milli Tesla) magnetic field is pointing due south.
Somebody throws an electrically charged baseball in a direction 23 east of
south, with a speed of 35.0 m/s. The charge on the baseball is 500C
(microCoulomb). What force will the magnetic field exert on the baseball
(magnitude and direction)? (Direction should be north, south, east, west, up, or
down.)
Ans: 9.71 X 10-5 Newtons, Up
7 A wire carries a current of 0.66 Amperes. This wire makes an angle of 58 with
respect to a magnetic field of magnitude 4.70 X 10-5 Tesla. The wire
experiences a magnetic force of magnitude 7.10 X 10-5 Newton. What is the
length of the wire?
Ans: 2.70 meters
8 A 20-km-long wire in space, moves with an orbital speed of 7600 m/s through
the earth’s magnetic field, whose magnitude is 5.10 X 10-5 Tesla. If the motion
is perpendicular to the magnetic field, what motional emf is developed across
the wire?
Ans: 7750 volts
9 A copper wire is formed into a circular loop whose radius is 8.29 cm. The loop
of wire is lying flat on an inclined plane whose angle of inclination is 41.0
above the horizontal. There is a magnetic field in that region, pointing
vertically upward whose magnitude increases from 1.83 T to 3.56 T in 1/3
of a second. Calculate the average emf (voltage) generated in the loop during
that time.
Ans: 8.46 X 10-8 Volt
10. In the LRC circuit shown below, calculate (a) the current through the circuit
and (b) the power used by the circuit. (1 nF = 1 X 10-9 Farad)
Ans: (a) 0.0196 A (b) 1.92 W
Ans: (a) 0.0196 A (b) 1.92 W