LAB: SERIES RESISTANCE
Please fill the blanks for full credit.
PURPOSE
Investigate resistance and determine the equivalent resistance of resistors in series. I suppose that you all know how to measure the current in a circuit and the voltage across element.
DISCUSSION
word bank: V/Reff, effective resistance, sum, resistances, drop, volts , resistors
A series circuit consists of ___________________ connected with the voltage source in such a way that all current travels through each resistor in turn. The effective resistance (or equivalent resistance), Reff, of a series circuit is the ____________ of the ____________ of the individual resistors in the circuit.
Where I is the circuit in amperes (A) , R is the _________________ _______ of the circuit in ohms (Ω ), and V is the voltage source in _______(V) .
power supply or dry cells, 8 connecting wires, voltmeter (0-5V), knife switch,
3 resistors (1K, 100K, 150K) , 0.5W or greater
milliammeter, 0-50mA or 0-100mA.
PROCEDURE
1) Connect in series the battery, the 3 resistors and the switch. close the switch. Break the circuit between the battery and the 1st resistor and measure the current using the multimeter. (insert the device between the battery and the resistor). 1 plug in COM and one plug in VmA. Turn the dial to 2000mA. (try 200mA if the current is really small). The unit is mA (milliampere) so you need to convert to A.
I1 = ______ mA = _______ A. (see diagram)
Now measure the current between the 1st and 2nd resistor. (break the circuit and insert the multimeter) I2 = _______A
(again, you need to open the circuit to insert the multimeter)
Measure the current between the 2nd and the third resistor. I3 = _______A
Measure the current between the 3rd and the switch resistor. I4 = _______A
conclusion:
2) Reconnect your resistors to have a close circuit. Measure the voltage drop across each individual resistor by connecting the voltmeter across each one in turn. You need to turn the dial to 20V. If the voltage is really small, try another scale. see figure.
V1 = _______V
V2= ________V
V3 = ________V
3) Find the voltage across the battery V = _________ V
Compare the sum V1+V2 + V3 to V. Discuss.
4) Using the your results (1 and 2) calculate the value of the resistors R1, R2, R3 using Ohm's law.
R1=V/I = ________Ω , R2 = V2/I = _________Ω , R3 = V3 / I = __________Ω
How do you know these values are right ? (compare to the numbers on each of the resistors)
5) using I, the current through the circuit and V the voltage drop across the group of resistors, calculate the effective resistance R. R = V / I = _________Ω
Compare this value to the sum R1 + R2+ R3 = __________Ω
conclusion in a circuit in series, the effective resistance is ___________________________________
TO GO FURTHER
1) A 4 ohm resistor and a 6 ohm resistor are connected in series with a 20 volt source.
A) draw the circuit diagram
B) find the current through the 4 Ω resistor.
C) the current through the 6 Ω resistor.
D) the voltage drop across the 4 Ω resistor.
E) The voltage across the 6 Ω resistor
2)
A) Find the effective (or total) resistance Reff = __________
B) the current in the circuit I = _______A = __________mA
C) The voltage drop across each resistance.
V1 = ___________ , V2 = ____________, V3 = ___________________
3) A set of miniature, decorative tree lights contains 50 individuals light bulbs of equal resistance, wired in series, and is designed for 120V operation. If the set uses 1A of current, what is the resistance of an individual light bulb and what is the voltage drop across each light bulb ?
Investigate resistance and determine the equivalent resistance of resistors in series. I suppose that you all know how to measure the current in a circuit and the voltage across element.
DISCUSSION
word bank: V/Reff, effective resistance, sum, resistances, drop, volts , resistors
A series circuit consists of ___________________ connected with the voltage source in such a way that all current travels through each resistor in turn. The effective resistance (or equivalent resistance), Reff, of a series circuit is the ____________ of the ____________ of the individual resistors in the circuit.
R = R1+R2 + R2
The potential difference across the voltage source is equal to the ______ of the voltage ______ across each resistor. V = V1 + V2 + V3
The
total current flowing in the circuit is mostly found by calculating the
equivalent resistance and then using the equation: I = _________Where I is the circuit in amperes (A) , R is the _________________ _______ of the circuit in ohms (Ω ), and V is the voltage source in _______(V) .
power supply or dry cells, 8 connecting wires, voltmeter (0-5V), knife switch,
3 resistors (1K, 100K, 150K) , 0.5W or greater
milliammeter, 0-50mA or 0-100mA.
PROCEDURE
Do not leave the switch close for more than a few seconds at a time.
1) Connect in series the battery, the 3 resistors and the switch. close the switch. Break the circuit between the battery and the 1st resistor and measure the current using the multimeter. (insert the device between the battery and the resistor). 1 plug in COM and one plug in VmA. Turn the dial to 2000mA. (try 200mA if the current is really small). The unit is mA (milliampere) so you need to convert to A.
I1 = ______ mA = _______ A. (see diagram)
Now measure the current between the 1st and 2nd resistor. (break the circuit and insert the multimeter) I2 = _______A
(again, you need to open the circuit to insert the multimeter)
Measure the current between the 2nd and the third resistor. I3 = _______A
Measure the current between the 3rd and the switch resistor. I4 = _______A
conclusion:
2) Reconnect your resistors to have a close circuit. Measure the voltage drop across each individual resistor by connecting the voltmeter across each one in turn. You need to turn the dial to 20V. If the voltage is really small, try another scale. see figure.
V1 = _______V
V2= ________V
V3 = ________V
3) Find the voltage across the battery V = _________ V
Compare the sum V1+V2 + V3 to V. Discuss.
4) Using the your results (1 and 2) calculate the value of the resistors R1, R2, R3 using Ohm's law.
R1=V/I = ________Ω , R2 = V2/I = _________Ω , R3 = V3 / I = __________Ω
How do you know these values are right ? (compare to the numbers on each of the resistors)
5) using I, the current through the circuit and V the voltage drop across the group of resistors, calculate the effective resistance R. R = V / I = _________Ω
Compare this value to the sum R1 + R2+ R3 = __________Ω
conclusion in a circuit in series, the effective resistance is ___________________________________
TO GO FURTHER
1) A 4 ohm resistor and a 6 ohm resistor are connected in series with a 20 volt source.
A) draw the circuit diagram
B) find the current through the 4 Ω resistor.
C) the current through the 6 Ω resistor.
D) the voltage drop across the 4 Ω resistor.
E) The voltage across the 6 Ω resistor
2)
A) Find the effective (or total) resistance Reff = __________
B) the current in the circuit I = _______A = __________mA
C) The voltage drop across each resistance.
V1 = ___________ , V2 = ____________, V3 = ___________________
3) A set of miniature, decorative tree lights contains 50 individuals light bulbs of equal resistance, wired in series, and is designed for 120V operation. If the set uses 1A of current, what is the resistance of an individual light bulb and what is the voltage drop across each light bulb ?