Alight ray strikes a plane mirror at an angle of 20 degrees to the normal. what is the angle of the reflected light ray to the normal?

40 degrees
70 degrees
0 degrees
20 degrees

20 degrees

Explanation:

According to the Law of Reflection, when a ray of light strikes a surface, the angle of this ray (incident ray) with respect to the normal of the surface is equal to the angle that forms the reflected ray with the same normal of the surface.  

In other words:  

Both the incident ray and the reflected ray and the normal to the surface are in the same plane, in addition, the angle of the incident ray is equal to the angle of the reflected ray.  

In this context, when a ray strikes the surface of a plane mirror, both the incident angle and the reflected angle will be the same.

see earlier

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