Solenoids
How coils of current-carrying wire create useful electromagnets
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Show Me The Physics YouTube Channel
Electric Bell Name the major parts of an electric bell. What is the function of part C?
Source: Elroy M. Avery School Physics (New York: Sheldon and Company, 1895) 556 Copyright: 2009, Florida Center for Instructional Technology. See license. | Clipart ETC | Alternate Sizes |
E - Electromagnet, H - Striker, P - Switch C - When the striker is attracted to the electromagnet, the circuit is opened and the striker returns to its initial position
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Ex 4) Magnetic field around Solenoid (Electromagnet)
(conductor arranged in a coiled pattern) North and South Pole 3D Solenoid Electromagnet
1. Determine North and South pole with ...
a) North Pole of a Compass
b) 2nd Left Hand Rule
Why Left and
not right?? Step 1 - Current travels from
DRAW the direction of the current on the wires
Step 2 - WITH PALMS AWAY, point the fingertips of left hand in direction of current
Step 3 - Thumb - North Pole!!
North Pole - RIGHT or LEFT???
Right
North Pole - Top or Bottom?
Bottom
North Pole - Right or Left?
Left
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Check Your Understanding
5 quick questions — pick an answer to see if you’re right.
1. A solenoid (electromagnet) is best described as:
2. In the 2nd left-hand rule, the left fingertips point along the current in the coils. What does the thumb point to?
3. In the left-hand rules on this site, which way does the current travel through the wire?
4. The current in an electromagnet is reversed. What happens to a nearby compass that was attracted to its north pole?
5. In an electric bell, what happens right after the electromagnet attracts the striker?
How an MRI Magnet Works
An MRI machine uses a large solenoid: a long coil with many turns of wire. When current flows, it produces a strong, nearly uniform magnetic field inside the coil where the patient lies.
Which statement describes the magnetic field of a long solenoid?
▶ Want a challenge? Open 6 more Regents-style questions (harder · mixed formats)
Challenge score: 0 / 6
C1. What happens to the solenoid’s poles if the current direction is reversed?
C2. Place a check mark in three boxes to indicate the changes that would make the magnetic field inside a solenoid stronger.
C3. A student makes the following claim.
Place a check mark in either the Support or Refute box. Justify your response.
C4. Suppose the MRI coil were made of ordinary copper wire with a total resistance of 0.10 Ω instead of superconducting wire. Determine the power that would be wasted as heat when the coil carries a current of 500. A.
C5. In a doorbell, pressing the button sends current through a solenoid, which pulls an iron rod to strike a chime. Why is the rod pulled in?
C6. MRI magnets use superconducting coils cooled by liquid helium. Identify one benefit and one drawback of this design compared with an ordinary copper-wire electromagnet.