6A Physics
Electricity CW 2023
Date due: 09/10/2023
Name: Jaden Small
Class: Physics-1
Instructions: Submit this assignment on folder/typing paper before or on the due date.
Marks will be deducted for late work.
1. a) Write Kirchhoff’s laws and state the physical basis of each [4 marks]
Kirchoff’s first law states that the total current flowing into a node is equal to the
total current flowing out of that node. This law is based on the law of conservation of
charge.
Kirchoff’s second law states that the total EMF is equal to the sum of all the potential
differences across all the resistances in the loop. This law is based on the law of
conservation of energy.
b) i) Find the branch currents flowing in the circuit below [6 marks]
60 = 10𝐼3 + 30𝐼2
60 = 10𝐼1 + 10𝐼2 + 30𝐼2
60 = 10𝐼1 + 40𝐼2
120 + 60 = 10𝐼3 + 20𝐼1
180 = 10𝐼1 + 10𝐼2 + 20𝐼1
180 = 30𝐼1 + 10𝐼2
60 = 10𝐼1 + 40𝐼2
−(180 = 30𝐼1 + 10𝐼2 ) × 4
6A Physics
Electricity CW 2023
60 = 10𝐼1 + 40𝐼2
−(720 = 120𝐼1 + 40𝐼2 )
−660 = −110𝐼1
−660
𝐼1 = −110
𝐼1 = 6𝐴
180 = 30(6) + 10𝐼2
180 = 180 + 10𝐼2
0 = 10𝐼2
𝐼2 = 0𝐴
𝐼3 = 𝐼1 + 𝐼2
𝐼3 = 6 + 0 = 6𝐴
ii) Find the potential difference between A and B. [3 marks]
𝑉𝐴𝐵 = 60 + 10𝐼3
𝑉𝐴𝐵 = 60 + 10 × 6
𝑉𝐴𝐵 = 60 + 60 = 120𝑉
Date due: 09/10/2023
6A Physics
Electricity CW 2023
2.
(i)
1
1 1
= +
𝑅3,4 4 3
1
3
4
7
=
+
=
𝑅3,4 12 12 12
1
7
=
𝑅3,4 12
12
𝑅3,4 =
7
1
1 7
+
𝑅5,3,4 5 12
1
12 35
=
+
𝑅5,3,4 60 60
1
47
=
𝑅5,3,4 60
60
𝑅5,3,4 =
47
=
𝑅𝑒𝑞 = 5 +
𝑅𝑒𝑞 =
60
47
235 60 295
+
=
𝑜𝑟 6.28Ω
47 47
47
Date due: 09/10/2023
6A Physics
Electricity CW 2023
(ii)
6
295
47 + 1
47
𝐼=
= 0.82𝐴
57
𝐼=
(iii)
47
×5
57
235
𝑉5 =
= 4.1𝑉
57
𝑉5 =
235 47
20
𝑉5(2𝑛𝑑) = 𝑉3 = 𝑉4 = 6 − (
+ )=
= 1.05𝑉
57 57
19
(iv)
235
47
𝐼5 = 57×5 = 57 = 0.82𝐴
20
4
𝑉5(2𝑛𝑑) = 19×5 = 19 = 0.21𝐴
20
20
20
5
𝑉3 = 19×3 = 57 = 0.35𝐴
𝑉4 = 19×4 = 19 = 0.26𝐴
Total: 25 marks
Date due: 09/10/2023