# Fleming's left-hand rule on charged particles

• moenste
In summary, the conversation discusses diagrams showing a magnetic field and different scenarios involving conductors and an electron moving within the field. The direction and magnitude of the forces are calculated using formulas and the Fleming's left-hand rule. The direction of the force on the electron is determined by the direction of the current. In the case of the electron, the left-hand rule must be modified due to its negative charge.
moenste

## Homework Statement

Diagrams (a) to (c) show a magnetic field of flux density 0.2 T directed perpendicularly into the paper. In each of (a) and (b) a conductor of length 0.3 m is entirely within the field and is carrying a current of 4 A in the plane of the paper. In (c) an electron is moving in the plane of the paper at 2 * 106 m/s. Copy the diagrams and show the direction of the force in each case. Also find the magnitude of the forces. (Charge on the electron = 1.6 * 10-19 C.)

Images:

2. The attempt at a solution
F = BIL sin θ
F = BQv sin θ

(a-b) F = 0.2 * 4 * 0.3 * sin 90 = 0.24 N
(c) F = 0.2 * 1.6 * 10-19 * 2 * 106 * sin 90 = 6.4 * 10-14 N

The (a-b) graphs we get using the Fleming's left-hand rule. For (c), however, I get the force directed in the opposite direction (to north-east, not south-west). I think this is because (in constrast to (a-b), where there was current in each case and not particle) the particle is directed downwards and thus is negatively charged, so we need to change the middle finger from south-east to north-west. But I'm not sure about that. Any ideas on (c) graph please?

Last edited:
If an electron is moving down and to the right, which way is the current?

moenste
haruspex said:
If an electron is moving down and to the right, which way is the current?
The opposite way, so upwards and left. And having this using the left-hand rule we get the correct answer. Right?

moenste said:
The opposite way, so upwards and left. And having this using the left-hand rule we get the correct answer. Right?
Yes.

moenste

## 1. What is Fleming's left-hand rule on charged particles?

Fleming's left-hand rule is a principle in electromagnetism that describes the direction of force on a charged particle moving in a magnetic field. It states that if the index finger, middle finger, and thumb of the left hand are extended perpendicular to each other, with the index finger pointing in the direction of the magnetic field, the middle finger in the direction of the particle's velocity, then the thumb will point in the direction of the force acting on the particle.

## 2. Who discovered Fleming's left-hand rule?

Fleming's left-hand rule is named after English scientist John Ambrose Fleming, who first described it in 1897.

## 3. What is the difference between Fleming's left-hand rule and right-hand rule?

Fleming's left-hand rule is used for charged particles moving in a magnetic field, while the right-hand rule is used for electric currents in a magnetic field. The two rules are similar in that they both use the direction of the field, motion, and force to determine the relationship between them.

## 4. How is Fleming's left-hand rule used in practical applications?

Fleming's left-hand rule is used to determine the direction of force on charged particles in devices such as electric motors, generators, and cathode ray tubes. It is also used in particle accelerators and other electromechanical devices.

## 5. Can Fleming's left-hand rule be applied to all types of charged particles?

Yes, Fleming's left-hand rule can be applied to any type of charged particle, including electrons, protons, and ions. As long as the particle has a charge and is moving in a magnetic field, the rule can be used to determine the direction of the force acting on it.

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