Which of the following best describes magnetic fields?

A. Magnetic fields need a conductor.

B. Magnetic fields are always found in insulators.

C. Magnetic fields have north and south magnetic poles.

D. Magnetic fields must have only positive charges.

An oil film on top of water has one patch that is much thinner than the wavelength of visible light. The index of refraction of the oil is less than that of water.

Under normal conditions, you are just barely able to lift a mass of 74 kg. Your friend drops a box of volume 2.4 m3 into a lake. If you are just able to lift it to the surface (so that it is still completely submerged), what is the mass of the box

How to find when a particle is speeding up and slowing down?

Work and energy have the same units because

Out of aluminum, copper, steel, and glass. Which material do you think will be the best thermal conductor?

A fountain of water and steam that erupts from the ground

A heavy rope, 50 ft long, weighs 0.5 lb/ft and hangs over the edge of a building 120 ft high. how much work is done (in ft-lb) in pulling half the rope to the top of the building?

Does adding a neutron to an atom's nucleus makes it an ion?

What is the difference between a fault-block and upwarped mountains?

Which of the following is not one of the reasons to properly warm up before exercising? A. Develop overall flexibility. B. Increase blood flow to the muscles and raise body temperature. C. Prevent injuries such as strains sprains and muscle cramps.