Electric & Magnetic Forces
Two charged balloons hang from strings. What question could you ask to observe the electric force between them?
“How does the distance between balloons affect how strongly they push or pull?”
What happens when current flows through a coiled wire around an iron nail?
The nail becomes an electromagnet that can attract magnetic objects.
What two main factors determine the size of magnetic forces?
Current strength and distance between objects.
What does it mean to “ask a testable question”?
It can be investigated by collecting data through observation or measurement.
Where are electromagnets used in everyday devices?
In doorbells, electric motors, speakers, and MRI machines.
Two bar magnets 2 cm apart attract each other. What happens to the force if they’re moved to 4 cm?
The force weakens because magnetic force decreases with distance.
From the data table: 100 wraps + 4 A = 0.8 T; 50 wraps + 2 A = 0.2 T. What trend do you see?
Note:
A (ampere) measures how much electric charge flows per second — basically, how strong the electric current is.
T (tesla) measures magnetic field strength.
Increasing wraps or current increases field strength.
Two magnets attract with 12 N of force. If the distance doubles, what happens to the force?
The force decreases greatly (inversely related to distance).
A student asks, “What happens if I add more batteries to my electromagnet?” Why is this a good scientific question?
It focuses on a variable that can be tested (measurable cause and effect).
A crane uses an electromagnet to lift cars at a junkyard. Why is an electromagnet better than a permanent magnet?
t can be turned on and off by controlling the electric current.
A magnet attracts a steel paperclip but not a wooden pencil. What question could you ask to investigate this?
“How does material type affect whether an object responds to a magnetic force?”
If two coils use the same current but different wire types, what question are you testing?
“How does wire material affect electromagnet strength?”
Students compare 50 wraps vs. 100 wraps. What cause-and-effect relationship should they notice?
More wraps → stronger field.
Students observe a motor spins faster with more batteries. What question should they ask next to extend their investigation?
“How does the number of wire turns affect motor speed?”
A student notices a speaker vibrates when music plays. What causes the movement?
The changing current creates a changing magnetic field that moves the speaker coil.
Students wrap 50 turns of copper wire around a nail and add another 50 turns. Predict how the field strength changes.
The magnetic field roughly doubles, because more wraps = more aligned domains.
Predict how switching from copper to aluminum wire affects strength and why.
Note: Aluminum has a higher resistance than copper.
Field decreases because aluminum has higher resistance → less current.
A student increases both wraps and batteries. What pattern should they expect in paperclips picked up?
The number of paperclips increases for both, but the current change (batteries) has a larger effect.
A group notices that their electromagnet gets warm. What question could they investigate to explain why?
“How does electric current affect the amount of heat produced in the wire?”
Compare the forces in an electric motor and a doorbell.
Both use electromagnetic forces; the motor creates rotation, the doorbell creates linear movement to hit the bell.
A student’s doorbell electromagnet weakens over time. Identify two possible causes and explain.
Low battery → less current; loose wire → higher resistance → weaker field.
You must lift a heavier object with your electromagnet. What two design changes would increase lifting ability?
Add more wraps and increase current (by adding batteries or improving connections).
Design a hypothesis about how magnetic force changes with distance.
If distance between magnets doubles, then the magnetic force will decrease to about one-fourth its original strength.
Create a testable question that connects current strength, magnetic field, and distance in one experiment.
“How does changing the distance between coils affect the strength of the magnetic field produced by different currents?”
Predict what would happen if the power supply in an MRI machine dropped by half.
The magnetic field strength would drop significantly, reducing image clarity and machine accuracy.