Download Current Electricity Practice 7 Name 1. A 20 ohm resistor and a 40

Current Electricity Practice 7
Name ____________________
1. A 20 ohm resistor and a 40 ohm resistor are connected in series to a 120 volt power supply.
a. Find V, I, R and P for all elements in the circuit.
b. What is the potential drop across the 40 ohm resistor?
c. How much power is dissipated by the 20 ohm resistor?
2. A 30 ohm resistor and a 50 ohm resistor are connected in parallel to a 120 volt power supply.
a. Find V, I, R and P for all elements in the circuit.
b. What is the potential drop across the 30 ohm resistor?
c. How much power is dissipated by the 50 ohm resistor?
3. A 20 ohm resistor and an unknown resistor are connected in series to a 100 volt power supply.
The current through the unknown resistor is 2 amps.
a. Find V, I, R and P for all elements in the circuit.
b. What is the resistance of the unknown resistor?
4. A 30 ohm resistor and a 70 ohm resistor are connected in parallel to a 10 volt power supply. An
ammeter is connected to measure the current through the 30 ohm resistor and a voltmeter is
connected to measure the potential drop across the 70 ohm resistor.
a. Draw the circuit, including the proper placement for the meters.
b. What will the ammeter read?
c. What will the voltmeter read?
5. A 40 ohm resistor and a 100 ohm resistor are connected in series to a power supply rated at 700
watts. An ammeter is connected to measure the current through the 100 ohm resistor and a
voltmeter is connected to measure the potential drop across the 40 ohm resistor.
a. Draw the circuit, including the proper placement for the meters.
b. What will the ammeter read?
c. What will the voltmeter read?
6. A 20 ohm resistor and a 40 ohm resistor are connected in parallel to a power supply. An ammeter
is connected to measure the current through the 20 ohm resistor and a voltmeter is connected to
measure the potential drop across the 40 ohm resistor. The voltmeter reads 60 V.
a. Draw the circuit, including the proper placement for the meters.
b. Find V, I, R, and P for all elements in the circuit.
c. What will the ammeter read?
7. A wire has a resistance of 3mΩ. What will the resistance of a wire with…
a. twice the length?
b. three times the cross sectional area?
c. three times the radius?
8. A 20 volt battery is connected to a 40 ohm resistor. How many electrons will flow through the
wire in 10 seconds?
9. A copper wire has a cross sectional area of 8 x 10-8 m2, and a length of 6 meters. What will be the
power dissipated in the wire if it is connected to a 3 volt battery? The resistivity of copper is 1.72
x 10-8Ωm.
Review Questions:
10. A metal object has a density of 8000 kg/m3, and a volume of 4 x 10-3 m3. It is submerged in water.
a. What is the object’s mass?
b. What is the buoyancy force on the object?
c. What is its acceleration?
d. If it sinks from rest, how long will it take to sink 2 meters?
e. When it comes to rest at the bottom, what will be the force between the object and the
ground?
11. A sample of gas is compressed from a volume of 4 x 10-3 m3 to 2.5 x 10-3 m3 at a constant
pressure of 1 atmosphere.
a. If the original temperature of the gas is 300 K, how many molecules are in the sample?
b. What is the temperature of the gas after the compression?
c. How much work was done on the gas? What the work positive or negative?
d. What is the change in internal energy for the gas?
e. How much heat was exchanged with the environment? Was heat absorbed or released by
the gas?
12. Use the diagram below to answer the questions:
a. What is the magnitude and direction of the net electric field at point P?
b. What is the net electric potential at point P?
c. At what other point (other than an infinite distance away) on the x-axis will the electric
potential be zero?