Force on a current-carrying conductor
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Question
What is the motor effect?
Answer
A wire carrying a **current** in a **magnetic field** feels a **force** (a sideways push) — the principle behind electric motors.
Question
State the equation for the force on a current-carrying wire.
Answer
$F = BIL\sin\theta$ — force = field strength × current × length × sin(angle between current and field). Given in the data booklet.
Question
In F = BIL sin θ, what is θ?
Answer
The **angle between the current and the magnetic field**. When the wire is perpendicular to the field, θ = 90° and sin θ = 1, so F = BIL.
Question
What is the unit of magnetic field strength B?
Answer
The **tesla (T)**.
Question
When is the force on a current-carrying wire the largest?
Answer
When the current is **at right angles** to the field (θ = 90°, sin θ = 1).
Question
When is the force on a current-carrying wire zero?
Answer
When the current runs **along (parallel to)** the field (θ = 0°, sin 0° = 0).
Question
State Fleming's left-hand rule.
Answer
On the **left** hand at right angles: **F**irst finger = **F**ield, se**C**ond finger = **C**urrent, thu**M**b = force/**M**otion.
Question
How are field B, current I and force F arranged?
Answer
All three are **mutually perpendicular** (at right angles to one another).
Question
What happens to the force if you reverse the current?
Answer
The **force reverses** direction. (Reversing the field does the same.)
Question
Double the current in a wire (field and length fixed) — what happens to the force?
Answer
The force **doubles** — F = BIL, so F is proportional to I.
Question
A 0.10 m wire carries 2.0 A at right angles to a 0.50 T field. Force?
Answer
F = BIL = 0.50 × 2.0 × 0.10 = 0.10 N.
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Topic 4.3 hub
Motion in electromagnetic fields
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