You have two lens A and B of focal length +50cm and -50cm respectively. The nature and power of the lenses respectively isa. Concave, -2 D ; Convex, +2 D b. Convex, +2 D; Concave, - 2 D

Concave, +2D

Convex -2D

Explanation:

Power of a lens is the reciprocal of its focal length.

For lens of +50cm = 0.5m

Power of the lens = 1/0.5

Power of the lens = +2Dioptres

Since the focal length is positive, the lens is concave

For the lens of -50cm = -0.5m

Power = 1/-0.5

Power = -2D dioptres

Since the focal length is negative, the lens is convex

adding a(n) to an electric circuit would increase the magnetic field around a wire;

b. solenoid

a solenoid is a type of electromagnet whose purpose is to generate a controlled magnetic field.

if the purpose of the solenoid is instead to impede changes in the electric current, a solenoid can be more specifically classified as an inductor rather than an electromagnet.