17 marks] Question 1
John and Tou take their toys down to a nearby pond to play. John has a toy boat made from wood. He
places the wooden boat on the pond and it floats. Tau, being a checky little boy, wants to make John's
wooden boat sink. So he attaches a piece of lead on one end of the string, and ties the other loose end onto
John's boat and gently places the lead into the water. Determine the smallest amount of lead (mass) that
will be enough to sink John's boat, assuming the specific gravity of wood is 0.5 and the density of the
pond water is equal to the density of pure water

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