Chapter 20: The Motor Effect Flashcards
How are electricity and magnetism related?
An electric current in a conductor produces a magnetic field around it.
How is force related to electromagnetism?
A force is exerted on a current-carrying wire in a magnetic field.
How do you increase the force on a current-carrying conductor in a magnetic field?
By increasing the strength of the magnetic field and/or the current
How do you construct an electromagnet?
A piece of wire is wrapped around a soft magnetic material. When there is a current in the wire, a magnetic field is induced in the metal.
What is the left hand rule?
MALTA FOOTBALL CLUB
Motion, Field, Current
Thumb, Forefinger, Middle finger
Use it in situations where you have field and current, and are trying to find motion.
What does a magnetic field around a straight wire look like?
A series of circles around the wire
What does a magnetic field around a solenoid look like?
Like a bar magnet
What is the magnetic field around a flat coil like?
Like a single wire, but there are two around each side.
What is the relationship between force and magnetic fields if a charged particle is travelling in parallel?
There is a force on a charged particle when it moves in a magnetic field as long as its parallel to the field, because there is no resistance if it is parallel.
What is the role of the split ring commutator in the d.c. motor?
It reverses the direction of the current every half turn as the coil passes through the vertical position, so that the coil keeps rotating in the same direction.
What does the brush contact do in the d.c. motor?
Brush contact provides electrical contact with the commutator. They are generally made of carbon, because they wear away slowly.
Explain how forces exerted on a current-carrying wire in a magnetic field makes a motor turn.
If there is a wire with a current running through in a magnetic field it will experience a force. In a DC motor, there is a wire in a magnetic field. The force it experiences turns it around, this turns a split ring commutator, where the charges goes from brushes into the wires.
Explain how forces exerted on a current carrying wire in a magnetic field make a loud speaker produce sound.
In a loud speaker, a coil is in a magnetic field. When current is run though it, the wire will experience a force that pushes it away from the field; this in turn pushes a cone, which makes the sound. Whatever frequency the AC current is at, the coil will move at that frequency, making a note of a certain pitch.
What factors affect the speed of a motor?
The current, the magnetic field
What factors affect the strength of an electromagnet?
Current, wrapping the wire into a coil or solenoid, putting a soft metal in the coil
