Lesson test: The magnetic field

Sign in

Libre University uses your GitHub account. Signing in is only needed to sit a final test, so the score is kept on your profile.

The magnetic field

1.[3p]
Why was the direction of the deflection in Oersted's 1820 experiment the startling part?

The needle set itself across the wire rather than towards or away from it, and no force law of the time produced a circulation

Correct

The needle moved at all, which no one expected

The answer is: The needle set itself across the wire rather than towards or away from it, and no force law of the time produced a circulation

The deflection reversed when the current was reversed

The answer is: The needle set itself across the wire rather than towards or away from it, and no force law of the time produced a circulation

The effect was too weak to be seen from the back of the room

The answer is: The needle set itself across the wire rather than towards or away from it, and no force law of the time produced a circulation

2.[2p]
A magnetic field can change the speed of a charged particle but not its direction.

True

The answer is: False

False

Correct

3.[3p]
A proton moves at $1.0 \times 10^{7}$ m/s perpendicular to a 2.0 T field. What is the radius of its circular path, in centimetres?

CorrectNot quite: 5.22

4.[3p]
Why does the cyclotron frequency not depend on the particle's speed?

A faster particle travels a proportionally larger circle, so the two effects cancel exactly

Correct

The magnetic force grows as the square of the speed

The answer is: A faster particle travels a proportionally larger circle, so the two effects cancel exactly

Because the magnetic force does no work

The answer is: A faster particle travels a proportionally larger circle, so the two effects cancel exactly

Because the field is uniform

The answer is: A faster particle travels a proportionally larger circle, so the two effects cancel exactly

5.[2p]
A velocity selector uses $E = 3.6 \times 10^{5}$ V/m and $B = 0.45$ T. What speed passes through undeflected, in units of $10^{5}$ metres per second?

CorrectNot quite: 8.0

6.[2p]
A straight wire carries 15 A through a 0.80 T field, with 0.35 m of it in the field and perpendicular to it. What force does it feel, in newtons?

CorrectNot quite: 4.2

7.[3p]
A coil of 200 turns and area 8.0 cm² carries 0.30 A in a 0.40 T field, with its plane parallel to the field. What is the torque on it, in newton metres?

CorrectNot quite: 0.0192

8.[2p]
What does the sign of the Hall voltage reveal that a measurement of current alone cannot?

Whether the charge carriers are positive or negative

Correct

The resistivity of the material

The answer is: Whether the charge carriers are positive or negative

The strength of the applied magnetic field

The answer is: Whether the charge carriers are positive or negative

Whether the current is steady or changing

The answer is: Whether the charge carriers are positive or negative

9.[3p]
Match each device to the principle it runs on.

Mass spectrometer
Velocity selector
Electric motor
Cyclotron

orbital period independent of speed
electric and magnetic forces cancel
torque on a current loop in a field
radius depends on mass over charge

Show the answer

Mass spectrometer: radius depends on mass over charge Velocity selector: electric and magnetic forces cancel Electric motor: torque on a current loop in a field Cyclotron: orbital period independent of speed

1.[3p] Why was the direction of the deflection in Oersted's 1820 experiment the startling part?

2.[2p] A magnetic field can change the speed of a charged particle but not its direction.

3.[3p] A proton moves at 1.0×107 m/s perpendicular to a 2.0 T field. What is the radius of its circular path, in centimetres?

4.[3p] Why does the cyclotron frequency not depend on the particle's speed?

5.[2p] A velocity selector uses E=3.6×105 V/m and B=0.45 T. What speed passes through undeflected, in units of 105 metres per second?

6.[2p] A straight wire carries 15 A through a 0.80 T field, with 0.35 m of it in the field and perpendicular to it. What force does it feel, in newtons?

7.[3p] A coil of 200 turns and area 8.0 cm² carries 0.30 A in a 0.40 T field, with its plane parallel to the field. What is the torque on it, in newton metres?

8.[2p] What does the sign of the Hall voltage reveal that a measurement of current alone cannot?

9.[3p] Match each device to the principle it runs on.

1.[3p]
Why was the direction of the deflection in Oersted's 1820 experiment the startling part?

2.[2p]
A magnetic field can change the speed of a charged particle but not its direction.

3.[3p]
A proton moves at $1.0 \times 10^{7}$ m/s perpendicular to a 2.0 T field. What is the radius of its circular path, in centimetres?

4.[3p]
Why does the cyclotron frequency not depend on the particle's speed?

5.[2p]
A velocity selector uses $E = 3.6 \times 10^{5}$ V/m and $B = 0.45$ T. What speed passes through undeflected, in units of $10^{5}$ metres per second?

6.[2p]
A straight wire carries 15 A through a 0.80 T field, with 0.35 m of it in the field and perpendicular to it. What force does it feel, in newtons?

7.[3p]
A coil of 200 turns and area 8.0 cm² carries 0.30 A in a 0.40 T field, with its plane parallel to the field. What is the torque on it, in newton metres?

8.[2p]
What does the sign of the Hall voltage reveal that a measurement of current alone cannot?

9.[3p]
Match each device to the principle it runs on.