The electric field near the surface of Earth points downward and has a magnitude of 150 N/C.
(a) Compare the upward electric force on an electron with the downward gravitational force.
? (upward force / downward force)
The gravitational force is is much larger?
The electric force is is much larger?
Both forces are equal?
.

(b) What magnitude charge should be placed on a penny of mass 6 g so that the electric force balances the weight of the penny near Earth's surface?
? C

(a) Electric field is much larger

(b)

Explanation:

An electron being negatively charged will experience a force in a direction opposite to that of the electric field, that is, the force will be upwards (electric field being downwards).

The force experienced by the electron due to the electric filed is given by:

Force due to gravity (downward direction):

Hence, the electric field is much larger.

It is given that a penny has mass

Gravitational force = mg = 0.05886 N

To balance that we have to put, say, q amount of negative charge on the penny. Therefore,

or,

electromagnetic shielding is the practice of reducing the electromagnetic field in a space by blocking the field with barriers made of conductive or magnetic materials. shielding is typically applied to enclosures to isolate electrical devices from their surroundings, and to cables to isolate wires from the environment through which the cable runs. electromagnetic shielding that blocks radio frequency electromagnetic radiation is also known as rf shielding.

the shielding can reduce the coupling of radio waves, electromagnetic fields and electrostatic fields. a conductive enclosure used to block electrostatic fields is also known as a faraday cage. the amount of reduction depends very much upon the material used, its thickness, the size of the shielded volume and the frequency of the fields of interest and the size, shape and orientation of apertures in a shield to an incident electromagnetic

from wikipedia