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CAIE A-Level Physics 20.2.2 Using F = BIL sin θ

Practise calculating magnetic force with F = BIL sin theta, rearranging it for unknown quantities and determining direction using Fleming’s left-hand rule.

Syllabus
2028–2030
Course
Physics 9702
Level
A2

Exam points

  • calculate force on a current-carrying conductor using F = BIL sin theta
  • rearrange the equation to determine B, I, L or angle and use consistent units
  • determine force direction using Fleming left-hand rule

20.2.2—The equation F = BIL sin θ, with directions as interpreted by Fleming’s question 1

[Maximum number: 5]

Question (a)

(a)

A second long, straight wire Q, carrying a current of 5.0 A out of the page, is placed parallel to wire P , as shown in Fig. 6.2.

Fig. 6.2

Fig. 6.2

The flux density of the magnetic field at wire Q due to the current in wire P is 2.6 mT .

[ 5 ]

Question (i)

(i)

Calculate the magnetic force per unit length exerted on wire Q by wire P.
force per unit length = Nm−1\mathrm{Nm}^{-1}

[ 2 ]

Question (ii)

(ii)

State the direction of the force exerted on wire Q by wire P.

[ 1 ]

Question (iii)

(iii)

The flux density of the magnetic field at wire P due to the current in wire Q is 1.5 mT . Determine the magnitude of the current in wire P. Explain your reasoning.
current = A

[ 2 ]
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