PHYS 202 Test #1 2/1/2012 Dr. Holmes NAME
DO ALL EIGHT PROBLEMS. THE WORTH OF EACH PROBLEM IS MARKED NEXT TO THE PROBLEM. SHOW YOUR WORK FOR PARTIAL CREDIT.
1) Consider two charged particles (q1 = +7 microCoul, m1 = 35 grams; q2 = +14 microCoul, m2 = 21 grams). The first particle is 4.5 cm to the West of the second one.
a) What is the magnitude and direction of the electric FORCE on the 1st
particle due to the presence of the 2nd particle? [When answering this direction question, answer with North,
East, South, West, Up or Down.]
435 Nt, West
b) Is the magnitude of the force on the second particle due to the first particle bigger, the same as, or smaller than the force on the first particle due to the 2nd particle?
Same.
c) Is the direction of the force on the first particle due to the 2nd particle the same or opposite that of the force on the second particle due to the 1st particle?
Opposite.
d) Is the magnitude of the acceleration of the second particle due to the presence of the first particle bigger, the same as, or smaller than the acceleration of the first particle due to the second particle? (Assume there are no other forces acting on the two particles.)
Bigger.
2) Consider the same two point charges as in problem #1: (q1 = +7 microCoul, m1 = 35 gm; q2 = +14 microCoul, m2 = 21 gm). The first particle is 4.5 cm to the West of the second one.
a) What is the electric field due to charge #1 at the location of charge #2 ?
3.11 x 107 Nt/Coul, East.
b) What is the voltage due to charge #1 at the location of charge #2 ?
+ 1.40 x 106 Volts .
3) a) What is the magnitude of the gravitational force between one proton and another proton when they are separated by 7.0 nm?
3.80 x 10-48 Nt.
b) What is the electrical force between one proton and another proton when they are separated by 7.0 nm?
4.70 x 10-12 Nt.
c) How much stronger is the electrical force than the gravitational force between the two protons at this distance (in other words, what is the ratio of the electric force to the gravitational force)?
1.24 x 1036 times stronger
4) An alpha particle (charge 3.2 x 10-19 C and mass of 6.64 x 10-27 kg) is to be accelerate4d from rest to a speed of 1 million miles per hour..
a) What voltage difference should be used if the acceleration is to be done electrically?
2,070 volts.
b) Should the alpha particle start out at the higher or lower voltage?
Higher.
c) If a voltage difference of twice that in part a) above is used, will the alpha be going: [less than twice as fast, twice as fast, more than twice as fast]?
Less than twice as fast.
5) A 16 microF capacitor has a voltage of 50 volts applied across it.
a) How much charge is stored on the capacitor?
8.0 x 10-4 Coul. = 800 microC.
b) How much energy is stored on the capacitor?
2.0 x 10-2 Joules = 20 mJ.
c) If the capacitor is a parallel plate type of capacitor, and the voltage applied to the plates is doubled (with everything else remaining the same), which of the following quantities will change (relative to the original 16 pF capacitor with 50 volts applied):
(1) capacitance, (2) energy stored, (3) charge stored?
[if none change, then answer none; if one changes, simply indicate which changes, if two change, then indicate both of those that change, if all three change then answer all]
2 & 3.
6) A particular light bulb is rated at 75 Watts when a voltage of 110 volts is placed across it.
a) What is the electric current through the light bulb in this circumstance?
0.682 amps.
b) What is the resistance of the light bulb?
161 W.
c) In designing a new wattage light bulb, should the resistance of the light bulb be lowered or raised from that in part b above if the power of the light bulb is to be increased when used with the same 110 volts power supply?
Lowered.
7) Consider three capacitors: C1 = 5 nF, C2 = 10 nF, C3 = 20 nF .
a) Connect the three capacitors in a circuit (make a circuit drawing) such that the effective capacitance is the smallest it can be:
b) Are the three capacitors above connected in series, parallel, or some other combination?
Series.
c) What is the effective capacitance of this circuit that has the largest effective capacitance using these three capacitors?
2.857 nF.
8) Consider three resistors: R1 = 5 W , R2 = 10 W , R3 = 20 W .
a) Connect the three resistors in a circuit (make a circuit drawing) such that the effective resistance is the smallest it can be:
b) Are the three resistors above connected in series, parallel, or some other combination?
Parallel.
c) What is the effective resistance of this circuit?
2.857 W
.
d) Connect the three resistors in a circuit (make a circuit drawing) such that the effective resistance is between 5 and 10 ohms.