Question

Mrs. Peterson assigned the students in her class a project to design a simple electric motor. Each student had to use a permanent magnet and an electromagnet made up of a coil of wire wrapped around an iron core. To be successful, the motor had to spin at least 150 times per minute. After the students designed their motors, each motor was connected to the same voltage source, and the number of turns the motor made in 5 seconds was counted. The table below describes each student's motor.

Electric Motor Designs

Student Name Number of Turns
in the Electromagnet's
Wire Coil Material of the Wire Coil Thickness of the Wire Used in the Coil Rate at Which the Motor Spins
Lupe 15 copper 0.4 mm 17 turns in
5 seconds
Sanjay 5 aluminum 0.4 mm 4 turns in
5 seconds
Oliver 5 copper 1.2 mm 21 turns in
5 seconds
Rebekah 15 aluminum 1.2 mm 11 turns in
5 seconds
Felipe 15 aluminum 0.4 mm 7 turns in
5 seconds

Which students met the criteria for success?
A.
Lupe, Oliver, and Rebekah only
B.
Lupe, Oliver, Rebekah, and Felipe only
C.
Lupe and Oliver only
D.
Lupe, Sanjay, Oliver, Rebekah, and Felipe
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Answer 1

Convert turns in 5 seconds to turns per minute: multiply by 12. The motor must reach at least 150 rpm, which is 150/12 = 12.5 turns in 5 seconds (so at least 13 turns).

Results:
- Lupe: 17 × 12 = 204 rpm — success
- Sanjay: 4 × 12 = 48 rpm — no
- Oliver: 21 × 12 = 252 rpm — success
- Rebekah: 11 × 12 = 132 rpm — no
- Felipe: 7 × 12 = 84 rpm — no

Answer: C (Lupe and Oliver only).