Tutorial 1 – Electrostatics

Course: FAD1022 Basic Physics 2
Semester: 2 2025/2026
Centre: Centre for Foundation Studies in Science, Universiti Malaya

Given Constants

  • Coulomb constant, $k = 9.0 \times 10^9 \text{ Nm}^2\text{C}^{-2}$
  • Electron charge, $q_e = 1.609 \times 10^{-19} \text{ C}$
  • Electron mass, $m_e = 9.11 \times 10^{-31} \text{ kg}$

Question 1

Figure 1 shows three charges $q_1$, $q_2$, and $q_3$ placed along a straight line.

Given:

  • $q_1 = 35\mu\text{C}$ (positive)
  • $q_2 = 10\mu\text{C}$ (negative)
  • $q_3 = 60\mu\text{C}$ (positive)
  • Distance $q_1$ to $q_2$: 20 cm
  • Distance $q_2$ to $q_3$: 40 cm

Determine the magnitude and direction of the net electrostatic force acting on:

a) $q_1$ b) $q_2$

Question 2

Figure 2 shows three point charges, $q_1$, $q_2$, and $q_3$ located in the x and y plane.

Given:

  • $q_1 = 35\mu\text{C}$ (negative)
  • $q_2 = 10\mu\text{C}$ (positive)
  • $q_3 = 60\mu\text{C}$ (positive)
  • Distance from $q_1$ to $q_2$: 0.7 m
  • Distance from $q_2$ to $q_3$: 0.5 m
  • Angle: $30°$

Determine the magnitude and direction of the net electrostatic force acting on $q_2$.

Question 3

Figure 3 shows three isolated point charges, $q_1$, $q_2$ and $q_3$, separated by distances AB and BC.

Given:

  • $q_1 = 6.5 \text{ nC}$ (positive)
  • $q_2 = 3.0 \text{ nC}$
  • $q_3 = 5.0 \text{ nC}$ (positive)
  • Distance AB: 15 cm
  • Distance from B to X: 5 cm
  • Distance from X to C: 30 cm

Determine the magnitude and direction of the electric field strength at point X.

Question 4

Based on Figure 4, calculate the magnitude and direction of electric field strength at point P.

Given:

  • $q_1 = 4 \text{ nC}$ (positive)
  • $q_2 = 9.5 \text{ nC}$ (positive)
  • $q_3 = 12 \text{ nC}$
  • Distance from $q_1$ to P: 1.8 m
  • Distance from P to $q_2$: 0.6 m

Question 5

An electron travelling at speed of $1.9 \times 10^7 \text{ m/s}$ enters the region between two parallel metal plates. The uniform electric field strength between the plates is $4.5 \times 10^3 \text{ NC}^{-1}$.

Given:

  • Initial velocity: $v = 1.9 \times 10^7 \text{ m/s}$
  • Electric field: $E = 4.5 \times 10^3 \text{ NC}^{-1}$
  • Plate separation: 22 mm
  • Plate length: 66 mm

Calculate:

a) Sketch the path of electron as it travels between the parallel plates. b) Calculate the acceleration of electron between the plates due to uniform electric field. c) Determine the horizontal and vertical components of electron's velocity as it emerges from the region between the plates. d) Calculate the angle of deflection of the electron beam as it exits the plates.

Additional Question

Figure 6 illustrates three point charges arranged in a shape of triangular configuration.

Given:

  • $q_1 = 6.0 \text{ nC}$ (positive) at position $(0.5\text{m}, 0)$
  • $q_2 = 2.0 \text{ nC}$ (positive) at position $(0, 0.5\text{m})$
  • $q_3 = 3.0 \text{ nC}$ (positive) at position $(0, -0.5\text{m})$

Calculate:

a) The magnitude and direction of force acting on charge $q_1$. b) The electric field strength acting at the location of $q_1$.

Related Concepts

  • Electrostatics
  • Coulomb's Law
  • Electric Field
  • Electric Force
  • Point Charge
  • Superposition Principle
  • Electron Motion in Electric Field

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