Basic Physics II Assignments

Start reading chapters 18 and 19 by September 21.  They go together, so you should read them at the “same time”.

Chapter 18:  Electric Current − Due Friday, October 2.

1.     1016 electrons flow past a point on a wire in 3s.  What was the current? 

2.     A current of 10mA flows through a resistor and the voltage across the resistor is 2V.  What is the resistance?

3.     A wire has a resistance of 10-5W per meter of length.  A current of 2000A flows down the wire.  A hawk is standing on the wire and its feet are 5cm apart.  What is the potential difference between its feet?  (This is why birds can survive standing on power lines; the potential difference across their body is small.)

4.     A copper wire has a resistance of 10-5W per meter of length at T = 20oC.

a)  What is the resistance of 1km of wire?

b)     What is the diameter of the wire?

5.     A platinum film resistor has a resistance of 100W at 20oC.  If I measure it resistance to be 98W,  what is the temperature of the resistor?

6.     A 9V battery is connected across a 200W resistor.  What is the power being delivered to the resistor?

7.     A 9V battery can produce a current of 300mA for one hour before “dying”.  How much energy was stored in the battery.  (The battery would be rated at 300mA∙hr.)

8.     A toaster is rated at 1500W when connected to the 120V power mains.  (Note that 1500W is the average power and 120V is the rms value since the voltage is sinusoidal.)  What is the resistance of the toaster? 

9.     A 200W resistor is connected to an 8Vrms voltage source.

a)     What is the peak current through the resistor?

b)     What is the peak power dissipated in the resistor?

c)     What is the rms current through the resistor?

d)     What is the average power dissipated in the resistor?

10.   A gallon of gasoline contains about 132 MJ of “available” energy. 

a)     How many kW∙hr is that? 

b)     If electricity is 11¢ per kW∙hr, what is the cost of 132MJ of electrical energy?  (Note that electrical motors are usually much more efficient than internal combustion engines, so this result may be a little misleading.)

 

Chapter 19:  Electric Circuits − Due Friday, October 9.

1.     You have three 150W resistors.

a)     What is the total resistance if they are connected in series?

b)     What is the resistance if they are connected in parallel?

2.     If R1 = 1.5kW, R2 = 2.0kW and E, the “voltage”, is 9V, what is the current through R2?

3.     Given the circuit at the right,

a)     What is the current supplied by the 3V battery in the circuit at the right?

b)     What is the current through the 500W resistor?

4.     Write down the equations resulting from Kirchoff’s rules for the circuit at the right.  Use the two loops ABCDEFA and CDEFC.  I’m not asking you to solve the equations, just write them down!  (The currents are positive in the directions shown by the arrows!)

5.     If I3 = 0 in the problem above, find V2/V1 in terms of R1 and R2.

6.    If I measure that VB – VA =  6V in the circuit at the right, what is the EMF of the battery?  Show its orientation in the circuit (draw it on your paper.)  

7.     The capacitor in the circuit at the right is initially discharged, i.e. Q = 0.  Then at t=0 the switch (S) is closed.  The resistor has a resistance of 10kW and it takes 0.05s for the voltage across the capacitor to reach 3V.  What is the value of C?

8.     Two capacitors in series have a total capacitance of 3mF.  One capacitor, C1, has twice the capacitance of the other, C2.  Find C1.

9.     Two capacitors in parallel have a total capacitance of 3mF.  One capacitor, C1, has twice the capacitance of the other, C2.  Find C1.