Charged Particle in Electric and Magnetic Fields

Let’s look at charged particles in electric and magnetic fields. Okay, so imagine you’re in a giant game of laser tag, and you’ve got your trusty laser gun at your side. But instead of just shooting lasers, your gun can also emit charged particles that you can use to your advantage.

Now, let’s say you’re facing off against a rival team who’s really good at dodging your lasers. Let’s say you create an electric field around them, you can now control the path of the electron. Suddenly, they can’t escape your electron attacks anymore, you can aim even after you have fired the electron.

But it’s not just about winning laser tag games. Charged particles in electric fields have real-world applications, too. They’re used in particle accelerators to study the fundamental nature of matter and in medical treatments like radiation therapy. In fact, the technology we described above is how computer displays work!

Charged particles in electric fields are not only useful for laser tag domination, but they have important scientific and medical purposes as well. Let’s learn about how charged particles interact in magnetic and electric fields.


  • An electron is a negatively charged particle. A proton is a positively charged particle
  • Opposites attract, a positively charged particle will be attracted to negative charges and vice versa.
  • Likes repel, a positively charged particle will be repelled by positive charges and vice versa.
  • A stationary charged particle will not interact with a magnetic field.
  • A moving charged particle will interact with a magnetic field.

Charged particle in Electric fields

Imagine you are a tiny little ball bouncing around a room. Suddenly, someone turns on an electric fan and points it at you. You’ll feel the wind blowing against you and pushing you in a certain direction. This is similar to how a charged particle, like an electron, feels when it’s in an electric field.

The electric field is like the wind from the fan, and it pushes the charged particle in a certain direction. If the particle is positive, it will be pushed in the opposite direction of the electric field. If it’s negative, it will be pushed in the same direction as the electric field.

Now, imagine that instead of a fan, you have a bunch of little people pushing and pulling on you. Each person represents a tiny bit of the electric field, and together they push and pull you in different directions. This is how the electric field affects the charged particle – it’s like a bunch of tiny forces all acting on the particle at once.

So the next time you feel a gust of wind or someone pushes you around, think about how a charged particle feels in an electric field!

After today you should now know how charged objects interact with other charged objects and with neutral objects?

  • Electrostatic force
    • Process of how objects become electrically charged
    • Interactions between charged particles
  • Electric field lines
    • simple point charges
    • pairs of charges
    • dipoles
    • parallel charged plates
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Question 1.

Diagrammatically, compare and contrast the interaction between two positive point charges, two negative point charges and a positive and negative point charge. [3 marks]

Question 2.

A student rubs a balloon against their head and notices the balloon sticks to their head, explain this phenomena. [3 marks]

Question 3.

Draw the path of an electron passing between a pair of charged plates, arrange the plates so the field lines are parallel to the horizon. [2 marks]

Question 4.

  • a) A charged plate has a 4 V potential difference with a spacing of 15 cm, if an electron is released midway between the plates, what is the maximum acceleration of the electron. [4 marks]
  • b) What is it’s maximum velocity [2 marks]
  • c) How would this differ if the electron was replaced by a proton. [4 marks]

Question 5.

A helium nucleus, consisting of two protons and two neutrons, is 5 cm from a proton.

  • a) Will this experience an attractive force or a repulsive force [1 mark]
  • b) What will be the magnitude of this force? [2 marks]


Questions 1.

Electric charge - Wikipedia
  • include diagram of like charges as well.

Question 4.

  • a) 4.7 * 1012 m/s/s towards positive
  • b) 8 * 106 m/s towards positive
  • c) Repeat calculations accounting for different mass and charge.

Question 5.

1.84 * 10^-29 N repulsion

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