Grade 10 Physical Sciences · Electricity and Magnetism

Calculate current or voltage from charge

Calculate current with I = Q/Δt or potential difference with V = W/Q (5 C passing in 2 s is a current of 2,5 A).

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Question 9.4 · May/June 2024 · Paper 2 · National (DBE) · 5 marks

The simplified diagram below represents the cell used for electroplating ornaments with silver, Ag. P and Q are the two terminals of the battery. Diagram for this question

9.4 Calculate the current needed to electroplate the ornament with

3, 25

g of silver in

30

minutes.(5)

Work it out on paper first. Then mark yourself with the official memo, one tick at a time.

More past paper questions: calculate current or voltage from charge

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3. Question 9.2.2 · November 2022 · Paper 2 · National (DBE) · 3 marks
The diagram below represents a simplified cell used for the electrolysis of CONCENTRATED chromium(III) chloride, $CrC ℓ_{3}$ (aq). Electrodes R and T are made of carbon.

The net cell reaction is: $2 CrC ℓ_{3} (aq) \to 2 Cr(s) + 3 C ℓ_{2} (g)$
9.2 The graph below, NOT drawn to scale, represents the changes in the mass of electrode T during electrolysis.
A current of $2, 5$ A passes through the cell for $10$ hours.

Calculate the:
9.2.2 Total charge that flows through the cell during this time(3)
Show the memo (3 ticks)Memo
1. ✓
  Formula $q = I Δ t$
  1 mark · Calculate current or voltage from charge
2. ✓
  Substitution $q = (2, 5) (10 \times 60 \times 60)$
  1 mark · Calculate current or voltage from charge
3. ✓
  Answer with unit $q = 9 \times 1 0^{4}$ C $(90000$ C $)$
  1 mark · Calculate current or voltage from charge
4. Question 7.3.3 · November 2023 · Paper 1 · Provincial · 3 marks
The circuit diagram below consists of four cells each with a voltage of $1, 5$ V. The resistance of bulbs A, B and C are $3 Ω$ , $6 Ω$ and $8 Ω$ respectively. Use the circuit diagram to answer questions that follow:

When switch S is closed, the reading on the ammeter is $0, 6$ A.
7.3 If the reading on $V_{3}$ is $4, 8$ V, calculate the:
7.3.3 Amount of charge that is passing through resistor C in $20$ s.(3)
Show the memo (3 ticks)Memo
1. ✓
  Formula $Q = I Δ t$
  1 mark · Calculate current or voltage from charge
2. ✓
  Substitution $Q = (0, 6) (20)$
  1 mark · Calculate current or voltage from charge
3. ✓
  Answer with unit $Q = 12$ C
  1 mark · Calculate current or voltage from charge
5. Question 8.3 · November 2022 · Paper 1 · Provincial · 3 marks
In the circuit diagram below, each cell has a voltage of $1, 5$ V. Use the diagram to answer the questions that follow.
8.3 Determine the magnitude of the charge that flows through $A_{1}$ in $6$ minutes.(3)
Show the memo (3 ticks)Memo
1. ✓
  Formula $I = \frac{Q}{Δ t}$
  1 mark · Calculate current or voltage from charge
2. ✓
  Substitution $1, 88 = \frac{Q}{360}$
  1 mark · Calculate current or voltage from charge
3. ✓
  Answer with unit $Q = 676, 8$ C
  1 mark · Calculate current or voltage from charge
6. Question 10.4 · November 2022 · Paper 1 · National (DBE) · 4 marks
Light is incident on the cathode of a photoelectric cell connected to a battery and a sensitive ammeter, as shown below.
10.4 The ammeter registers a constant current of $0, 012$ A.

Calculate the minimum number of photons of light that strike the cathode in a $10$ s period.(4)
Show the memo (4 ticks)Memo
1. ✓
  Charge that flows $q = I Δ t = (0, 012) (10) = 0, 12$ C
  1 mark · Calculate current or voltage from charge
2. ✓
  Substitution of $0, 12$ C $n = \frac{Q}{e} = \frac{0 , 12}{\dots}$
  1 mark · Calculate shared charge and electrons transferred
3. ✓
  Substitution of $e$ $n = \frac{0 , 12}{1 , 6 \times 1 0 ^{- 19}} = 7, 5 \times 1 0^{17}$ (electrons)
  1 mark · Calculate shared charge and electrons transferred
4. ✓
  Number of photonsNumber of photons $= n = 7, 5 \times 1 0^{17}$
  1 mark · Explain the photoelectric effect

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