Grade 11 Physical Sciences · Electricity and Magnetism

Calculate electric field strength

Calculate electric field strength using E = F/q or E = kQ/r², or the force on a charge in a field.

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Question 1.7 · May/June 2025 · Paper 1 · National (DBE) · 2 marks

Various options are provided as possible answers to the following questions. Each question has only ONE correct answer. Choose the answer and write only the letter (A–D) next to the question numbers (1.1 to 1.10) in the ANSWER BOOK, e.g. 1.11 E.

1.7 R and S are two small charged spheres placed a distance apart. P is a point to the right of sphere S.

E_{R}

and

E_{S}

are the electric fields at point P due to the charges on spheres R and S respectively. See the diagram below.

Which ONE of the following combinations is CORRECT for the net charge on spheres R and S?(2) Diagram for question 1.7

A Sphere R: Positive; Sphere S: Negative
B Sphere R: Negative; Sphere S: Positive
C Sphere R: Negative; Sphere S: Negative
D Sphere R: Positive; Sphere S: Positive

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More past paper questions: calculate electric field strength

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3. Question 7.1 · November 2024 · Paper 1 · National (DBE) · 3 marks
P is a $+ 2$ nC point charge. X is a point $6$ cm away from charge P, as shown in the diagram below.
7.1 Calculate the magnitude of the electric field at X.(3)
Show the memo (3 ticks)Memo
1. ✓
  Formula $E = \frac{k Q}{r ^{2}}$
  1 mark · Calculate electric field strength
2. ✓
  Substitution $E = \frac{( 9 \times 1 0 ^{9} ) ( 2 \times 1 0 ^{- 9} )}{( 0 , 06 ) ^{2}}$
  1 mark · Calculate electric field strength
3. ✓
  Answer $E = 5 \times 1 0^{3}$ N·C $^{- 1}$ ( $5000$ N·C $^{- 1}$ )
  1 mark · Calculate electric field strength
4. Question 1.7 · May/June 2024 · Paper 1 · National (DBE) · 2 marks
Various options are provided as possible answers to the following questions. Each question has only ONE correct answer. Choose the answer and write only the letter (A–D) next to the question numbers (1.1 to 1.10).
1.7 The magnitudes of electric fields generated by different point charges are measured at a fixed point. For each measurement, the distance between this fixed point and the charges are the same.

Which ONE of the following sketch graphs CORRECTLY shows the relationship between the magnitude of the electric field (E) and the magnitude of the charge (Q)?(2)
1. A
2. B
3. C
4. D
Show the memo (1 tick)Memo
1. ✓
  Choose the correct option $E = \frac{k Q}{r ^{2}}$ . With r fixed, $\frac{k}{r ^{2}}$ is a constant, so $E \propto Q$ : a straight line through the origin.
  
  Answer: A
  2 marks · Calculate electric field strength
5. Question 7.1.2 · May/June 2024 · Paper 1 · National (DBE) · 3 marks
7.1 X is a point $0, 025$ m away from a $+ 4$ nC point charge. See the diagram below.
7.1.2 Calculate the magnitude of the electric field at point X.(3)
Show the memo (3 ticks)Memo
1. ✓
  Formula $E = \frac{k Q}{r ^{2}}$
  1 mark · Calculate electric field strength
2. ✓
  Substitution $E = \frac{( 9 \times 1 0 ^{9} ) ( 4 \times 1 0 ^{- 9} )}{( 0 , 025 ) ^{2}}$
  1 mark · Calculate electric field strength
3. ✓
  Answer with unit $E = 5, 76 \times 1 0^{4}$ N·C $^{- 1}$ ( $57600$ N·C $^{- 1}$ )
  1 mark · Calculate electric field strength
6. Question 7.4 · November 2023 · Paper 1 · National (DBE) · 3 marks
Two point charges, $A$ and $B$ , each with a charge of $+ 3 \times 1 0^{- 9}$ C, are stationary on a horizontal surface. Point $P$ is r metres from charge $A$ and 2r metres from charge $B$ , as shown in the diagram below.
7.4 Calculate the magnitude of the net electrostatic force that an electron would experience if placed at point $P$ .(3)
Show the memo (3 ticks)Memo
1. ✓
  FormulaOption 1:
  $F = Eq$
  1 mark · Calculate electric field strength
2. ✓
  Substitution $= (27) (1, 6 \times 1 0^{- 19})$
  1 mark · Calculate electric field strength
3. ✓
  Answer with unit $= 4, 32 \times 1 0^{- 18}$ N
  1 mark · Calculate electric field strength

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