General Physics
1. A 6 V battery is connected to the circuit shown below. Answer the following questions for the combination of resistors shown.
a) Find the equivalent resistance for this circuit.
b) How much current is drawn from the battery by the circuit?
c) How much energy does the battery provide in 5 hours?
d) How much power is dissipated in the 200 W resistor?
2. Consider the circuit drawn below which is composed of resistors and ideal battery sources.
a) Calculate all of the currents flowing in this circuit.
b) How much power is used by the 212 W resistor?
c) How much power is supplied by each of the batteries?
d) Find the heat energy produced by the 212 W resistor in 2 days.
e) The 710 V ideal battery is replaced by a real battery with an EMF of 710 V and internal resistance of 1 W (note that the currents in the circuit are not affected much by this added resistance). What is the terminal voltage of the real battery?
3. A space heater coil is made from a 50 meter length of wire of radius .0007 m. The resistance of the wire is measured to be 5 W at 30 oC and the temperature coefficient is found to be 7x10-3 oC-1. Answer the following questions for the situation described.
a) The heater is connected to a 120 Volt power source during operation, and heats up to a temperature of 1700 oC. What is the resistance of the wire during operation?
b) How much current flows through the heater wire during operation?
c) Find the resistivity of the wire during operation?
d) When the heater wire is connected to a 50 V power supply, it heats up to 500 oC. How much power does the heater use in this case?
e) A 240 V power supply is connected to the heater wire. Calculate the resistivity if 40 A is measured in the wire.
4. Answer the following questions for the circuit shown below.
a) Reduce the above circuit to a single equivalent resistance and a voltage source. In other words, calculate the equivalent resistance for the above combination of resistors.
b) How much current is drawn from the battery?
c) How much energy is provided to the battery in 10 seconds?
5. Consider the circuit shown below. The batteries in the circuit contain a negligible internal resistance. Draw all currents and the directions of each flowing in the circuit branches.
1 kW
a) Find all of the currents flowing through the circuit. You must show the direction of flow in the schematic to recieve full credit.
b) How much power is lost to heating up the 1 kW resistor?
c) How much power is delivered from each of the individual batteries?
d) How much power is provided to the resistances in the circuit. That is, what is the total power lost to Joule heating?
6. A hair dryer is constructed by attaching a coil of wire to a constant 120 V power supply. The special wire (resistivity of 4.4x10-7 W. m and temperature coefficient of 1.4x10-3 C-1, at 20oC) used to make the heater coil is 500 m long with a cross-sectional area of 4x10-5 m2.
a) Find the resistance of the heater coil before it is turned on, assuming room temperature is 20oC.
b) What is the resistance of the heater coil if it heats up to 800oC during operation?
c) How much heat is dissipated in the wire during operation?
d) At another heat setting, the current through the heater coil is 15.5 A. How much power is lost to Joule heating?
e) Calculate the resistivity and resistance of the coil if 6A flows through the heater coil. (2answers)
7. Answer the following questions for the circuit shown below. The resistances shown are in ohms.
a) Find the total equivalent resistance for the circuit above.
b) What current is provided by the battery?
c) How much total power is used for the resistances in this circuit?
d) If the battery can provide 120 Amp-hours before going dead, then how long will the battery last?
8. Refer to the figure below for this problem. The resistors have units of ohms and the values for the batteries are in volts (standard SI units). Be sure to indicate the directions of your currents to clarify your answer.
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