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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 500C (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