2. A junction is a point where two or more wires (or lines in a circuit diagram)
ID: 1428087 • Letter: 2
Question
2. A junction is a point where two or more wires (or lines in a circuit diagram) connect. For example, Kirchhoff’s Junction Law states that the sum of currents entering a junction must equal the sum of currents leaving the junction. To apply Kirchhoff’s Junction Law the direction of the current in each wire must be designated. Consider the following circuit. Since conventional current flows from + to - the current I from the power supply enters junction “a” from the left. Kirchhoff’s Junction Law therefore requires that the sum of the currents flowing through R1 and R2 equal current I.
A student measures the potential difference across R1(600 ?) and recordsV1= 5.8 ± 0.2 V. A measurement of the current through R2 (300 ?) gives I2 = 20 ± 1 mA.
a) Determine the current through R1 with its uncertainty.
b) Determine the current I with its uncertainty.
c) Compare your value of I (with uncertainty) to a measured value of 31 ± 1 mA.
3. Two resistors R1 and R2 (where R1 has twice the resistance of R2 , R1 = 2R2) are connected, along with a battery, in two arrangements as shown. An identical potential difference V across the battery produces a current I in each circuit (note the current I is different in each circuit). For each circuit fill in the blanks below to show the relations between the currents and potential differences in each resistor.
Connection Type:
Current (in terms of I)
R1:
R2:
Potential Difference (in terms of V)
R1:
R2:
4. a) In the following circuit the ammeter reads 0.1A with the switch closed. Select the correct current for each position.
b) In the following circuit the ammeter reads 0.2A with the switch closed. Select the correct current for each position.
R2 R1Explanation / Answer
Q2
a) current through R1 = I2 / 2 = 10 +- 0.5 mA
b) current through battery I1 + I2 = 30 +- 1.5 mA
Q3
series connection (figure on the left)
current through R1 = I
current through R2 = I
potential difference across R1 = 2V/3
potential difference across R2 = V/3
parallel connection (figure on the right)
current through R1 = I/3
current through R2 = 2I/3
potential difference across R1 = V
potential difference across R2 = V
Q4 a)
current at position 1 is equal to 0.1 A
current at position 2 is equal to 0.1 A
current at position 3 is equal to 0.1 A
Q 4 b)
current at position 1 is equal to 0.2 A
current at position 2 is equal to 0.1 A
current at position 3 is equal to 0.1 A
current at position 4 is equal to 0.2 A
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