Flashcards in Conceptual Physics-Magnetism Unit-Test Deck (45):
What is the basic cause of magnetism?
Moving Electrons and magnetic domains. Moving electrons case large groups of atoms to have all their North and South poles aligned. These are called magnetic domains. When all the domains in an object have the same orientation, it is magnetized.
What does the basic cause of magnetism explain?
Why, when a magnet is split, two new magnets with their own north and south poles are created, and how objects can become magnetized.
Is the Earth a magnet?
What is a compass?
A small device that uses a magnet to line up with the Earth's north and south poles.
What is a magnetic field?
It is an area where the magnetic force is the strongest, but it is even stronger at the poles.
How is a magnetic field shaped?
Oval, arcs going from one pole to another
circular around a wire with current running through it.
What happens when current moves through a wire?
A magnetic field is created around it because the domains are aligned by the current.
What are the similarities and differences between a permanent magnet and an electromagnet?
They are similar because they both have north and south poles. They are different because only the electromagnet can switch poles, vary its strength, be turned off and on, and needs a source of electricity.
How does a galvanometer detect the presence of an electric current?
When a current runs through its coils a magnetic field is created which deflects the needle. It shows the direction of current by the direction the needle moves. It is a small magnet which is attracted to the field around the wires.
How can the strength of an electromagnet be increased?
You can add coils, increase the current, or increase the size of the core.
How does an electric current cause a motor to move?
Current goes through an electromagnet on the armature, which causes it to change poles when the commutator switches the current. The poles are attracted and repelled by the field magnets, and it moves in a circular motion.
How does a generator convert kinetic energy to electrical energy?
It turns wires within a larger magnetic field, taking kinetic/moving energy from wind or water or other sources.
How does the idea of conservation of energy relate to the operations of motors and generators?
No energy is lost, it is just converted from kinetic to electrical and vice versa. It does not create energy from nothing.
What causes a generator to produce an alternating current?
As the wire turns and cuts through the flux lines perpendicularly to the magnetic fields, it produces current first in one direction then the other.
What is the difference in the process of generating electricity by using coal compared to using wind energy?
Coal is burned to heat water which creates steam which turns a turbine. Wind directly turns and turbine and is renewable.
What is the difference between renewable and nonrenewable energy sources?
Renewable energy can be replaced within a lifetime, nonrenewable cannot. Renewable is also always available.
What are the principle parts of a motor?
The field magnets, armature, comutator and brushes
Define field magnets
two magnets which attract and repel the armature.
a solenoid that rotates within the field magnets.
two metal arms that touch the metal base of the commutator and provide current from the batteries
What role does the commutator play and why does it need to have a split in it?
The commutator switches the batteries direct current into alternating current. The split keeps the positive and negative terminals separate.
Why is an electromagnet essential in the armature of this type of motor?
The motor has to turn the armature, and because the electromagnet cans witch poles, each side of the armature is attracted to one magnet, and then the other, so that it rotates.
Is the direction of rotation of the armature affected by reversing the direction of current?
Is the direction of rotation of the armature affected by reversing the field poles?
Why must the field poles have unlike polarity?
If they didn't the armature would be attracted or repelled by both magnets at the same time so it wouldn't move.
What form of energy is supplied to the motor?
What form of energy is delivered by the motor?
How does this apply to the law of conservation of energy?
The energy from the battery does not go away and the energy to move the armature does not just appear from thin air. All the electrical energy becomes mechanical energy.
Define magnetic domains
Groups of atoms with their magnetic poles lined up based on how their electrons spin around them
In magnetized objects, the magnetic domains...
line up with their north and south poles facing the same direction.
The magnetic domains... in Unmagnetized Objects
do not line up
Magnetic domains explain why a magnet might become demagnetized by dropping it. Why?
The domains are "jumbled" by the impact.
How can something be demagnetized?
How could a pin be magnetized?
If the domains were lined up, usually by stroking it on a magnet in the same direction lots of times.
A current carrying coil of wire with many loops
A solenoid with a ferromagnetic core (like iron nails)
How does what you learned about magnetic domains and electrons relate to how you can use current, more turns of wire, or a bigger core to increase the strength?
Electrical current aligns magnetic domains
More wire creates more magnetic fields
Iron is magnetic, so it amplifies the power of the solenoid.
What is a galvanometer
it is a device that detects current
How can a magnet be used to induce (create) current?
It creates current when a magnet and wires move through/around/near/within each other
When a wire is moved across magnetic field lines...
a current is induced in the wire.
The amount of current induced in a moving wire depends on...
the speed of the wire, the amount of wire, and the strength of the magnetic field in which the wire is moving.
What are some examples of potential sources of kinetic/mechanical energy?
Wind, water, steam