Steven buys a pair of scissors instead of getting a haircut. He belives the scissors will last for a long time, while the haircu
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Answer:
The magnitude of the force, B = 5 Tesla, Up (North) direction
Explanation:
Magnetic force F= Eq where Electric field, E = 750 NC
and charge, q = -70 μC = -7 ×C
F = 750 × -7 ×
F = 0.0525
But F = qvB; B =
where B is the magnetic field
= 0.0525 ÷ ( -7 × × 30)
B = 5.0 Teslas
The force on a negative charge is in exactly the opposite direction to that on a positive charge.
Hence the direction of the charge is up (North).
The electron is accelerated through a potential difference of 
, so the kinetic energy gained by the electron is equal to its variation of electrical potential energy:
where
m is the electron mass
v is the final speed of the electron
e is the electron charge
is the potential difference
Re-arranging this equation, we can find the speed of the electron before entering the magnetic field:
Now the electron enters the magnetic field. The Lorentz force provides the centripetal force that keeps the electron in circular orbit:
where B is the intensity of the magnetic field and r is the orbital radius. Since the radius is r=25 cm=0.25 m, we can re-arrange this equation to find B:
where
m is the electron mass
v is the final speed of the electron
e is the electron charge
Re-arranging this equation, we can find the speed of the electron before entering the magnetic field:
Now the electron enters the magnetic field. The Lorentz force provides the centripetal force that keeps the electron in circular orbit:
where B is the intensity of the magnetic field and r is the orbital radius. Since the radius is r=25 cm=0.25 m, we can re-arrange this equation to find B: