Electricity and Magnetism Quiz

Which of the following devices use a solenoid as a primary part of the device?

• induction ovens

• generators

• electric motors

• electronic door locks

Answer explanation

A solenoid consists of a coil of wire around a movable, central iron core. Electronic door locks function because of solenoids. When current flows through the solenoid, the central pole is pushed out of the coil, unlocking the door.

Solenoids are not a primary part of an electric motor, although one may be used to activate a motor.

What makes iron ferromagnetic, whereas most other materials are not?

• a very small valence shell

• an unequal number of electrons and protons

• excess neutrons in the nucleus

• similar electron spin directions

Answer explanation

Iron is ferromagnetic because four of its electrons spin in the same direction. In most materials, pairs of electrons spin in opposite directions, so electron spin cancels out. Moving charge, even spinning electrons, produces magnetism.

what is ferromagnetic

• Ferromagnetic materials cannot be magnetized.
• Ferromagnetic materials lose their magnetization immediately.
• Ferromagnetic materials are only found in non-metallic substances.
• Ferromagnetic materials are those that can be magnetized and retain their magnetization.

Most materials with paired electrons are considered "diamagnetic," meaning they are weakly repelled by a magnetic field

In most materials, pairs of electrons spin in

• opposite directions
• no specific direction
• random directions
• the same direction

Iron is ferromagnetic because four of its electrons spin

• Iron's ferromagnetism is caused by its metallic bonding.
• Iron is ferromagnetic because it has unpaired electrons that can align their spins.

• Iron is ferromagnetic because it has a high melting point.
• Iron is ferromagnetic due to its high density.

Answer explanation

Because they align, they spin in the same direction. Better for ferromagnetic meaning they are going to be charged and keep that charge longer

One charged particle is held in place while a second charged particle is brought near and released. The second particle moves away from the first particle. Which of the following conclusions can be made based on this information?

• One particle was neutral and the other had an electrical charge.

• The particles were oppositely charged.

• The particles had the same type of charge.

• Both particles were neutral.

Answer explanation

Only particles with the same type of charge will repel. One particle moved because the other was fixed in place.

If a metal wire is magnetic and attracts metallic objects, it can be concluded that:

• there is an electric current moving through the wire

• the wire is permanently magnetic

• the wire would repel non-metallic objects

• the wire is copper

Answer explanation

Moving electric charges drive magnetic fields, so if the wire is magnetic and attracts metal, it must be conducting an electric current.

Electromagnets can be formed entirely from nonmagnetic materials. How can an electromagnet have magnetic properties if electricity and magnetism are not the same thing?

• Electromagnets only work if they have an iron core. Iron can be magnetized.

• Charges in the nonmagnetic material become magnetic when they are moving.

• 
  The resistance in the copper wire of an electromagnet makes the charges magnetic.

Answer explanation

All moving charges have a magnetic field. Once the charges stop moving, the magnetic field disappears.

A home is decorated with a string of lights. One of the light bulbs burns out, but the rest stay lit. Which type of circuit is this an example of?

• bridge

• series

• parallel

Answer explanation

In a parallel circuit, if one circuit is broken, the rest remain intact and functional.

What resistance is needed to obtain a 2 mA current in a circuit powered by a 9V battery?

• 6000 ohms
• 4500 ohms
• 4.5 ohms

• 18 ohms

Answer explanation

According to Ohm's law, voltage V equals current I times resistance R.

V = IR

Solve for resistance, R:

R = V/I

Identify the givens and write each in standard units:

V = 9 V

I = 2 mA = 0.002 A

Substitute values and solve:

R = (9 V) / (0.02 A) = 4500 Ω

Convert the current into amperes before solving for resistance.