Download When no current is present, all the compass

1. What happens to a compass needle when it comes in close contact of an electric
current? What happens when that current is reversed?
When no current is present, all the compass needles will point in the same
direction (toward Earth’s magnetic field). When there is a current present, all the
compass needles move to align with the magnetic field created by the electric current. If
the current is reversed, each needle will point in the opposite direction.
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Figure shows how the magnetic field around the
current-carrying wire forms a circle around the wire.
2. Explain the right-hand rule. Why is it used?
“If you hold a wire in your right hand and point your thumb in the direction of the
positive current, the direction that your fingers curl is the direction of the magnetic
current.” This rule is used to determine the direction of a magnetic field; clockwise or
counterclockwise. Keeping in mind that the direction of the electric current is OPPOSITE
to the direction that the electrons are flowing!!!
●
Current through wire is moving upward
(electrons are moving downward) and magnetic field
is moving counterclockwise because that is the
direction of the right hand finger curl.
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Increasing the current will INCREASE the
magnetic force.
●
The net force being exerted is perpendicular to
the current.
3. Why is a solenoid used to create a stronger magnetic field? What does it resemble?
To increase the magnetic force from the presence of a current, without increasing
the current (because that is often dangerous), you can wrap a wire into a coil. This is
called a solenoid and it is MUCH safer. By creating a solenoid, the magnetic field of each
loop of wire adds to the strength of the magnetic field of any neighboring loops. Thus
creating a stronger magnetic field, similar to a bar magnet.
● More loops and a stronger current will create a
stronger magnetic field.
4. What is an electromagnet? Why is it used?
By inserting a rode made of magnetic material, such as iron, through the center of
the coils in a solenoid, the strength of the magnetic field can be increased. This is called
an electromagnet.
● The magnetic field of the solenoid caused the rod to also
become a magnet.
● An electromagnet is STRONGER magnet than a solenoid
because the rod adds to the coil’s magnetic field.
5. How do electric motors work?
Electric motors are machines that convert electrical energy into mechanical
energy. They can perform work when attached to an external device. These can be found
in many devices around your home (toys, washing machines, dryers, fans, etc.)
●
Commutator causes current to change
direction. Thus causing the magnetic field to
change direction as the coil spins. This needs to
happen because the repulsion of the north and
south poles surrounding the coil. Without this
constant change in direction, the loop would
simply bounce back in forth in the magnetic
field until the force of friction caused the loop to
come to a rest. Because the current keeps
reversing, the loop rotates in one direction.
Cause
Effect
Current in the coil
Magnetic field
Magnetic field of wire
Wire spins
Slits in the commutator
Change in direction of current
Reversal of current
Wire rotates in one direction
6. How does a galvanometer work?
A galvanometer is a device used to measure current. It consists of a coil of
insulated wire wrapped around an iron core that can rotate between poles of a permanent
magnet (an electromagnet). This can also function as an ammeter, which measures
current and voltage.
● The magnetic field of the electromagnet interacts with
the magnetic field of the surrounding permanent magnet,
resulting in a force that turns the core, which moves a
needle along a scale to show current in amperes.