You are observing a 20 cm-tall object in a pinhole camera (with a screen at the end like those you used in lab/recitation this week). The screen is 25 cm from the pinhole. The image on the screen is 5 cm tall. (Note: try to do this problem without a calculator since the calculations involved are the type you would be expected to be able to do on an exam without using a calculator.) 1. If you moved the screen farther from the the pinhole, the image on the screen would:

a. Stay in focus but decrease in size
b. stay in focus but increase in size
c. lose focus

2. If you were looking at two objects, one 50 cm from the pinhole and one 75 cm from the pinhole, which object would be in 'focus' on the screen?

a. Can't determine from the information
b. the 50 cm object would be in focus
c. both objects would be in focus
d. the 75cm object would be in focus

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