In which of the following is no work done a. climbing stairs b. lifting a book c. pushing a shopping cart d. none of the above

The answer is D.

Explanation:

Look at these options. Do all of these require effort? Yes. If you were to push a shopping cart, do you have to apply force? if you were to lift a book, do you indeed move the book, does it exert force? While walking up stairs, do you have to move your legs uphill, is there force used? All of these require input, and force. Most things in life require work, unless we have a machine to do it for us.

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

answer is slate

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