What is a necessary condition for total internal reflection in a medium?
a. when the angle of incidence is equal to the critical angle
b. when the angle of incidence is greater than the critical angle
c. when the angle of refraction is equal to the critical angle
d. when the angle of reflection is less than the critical angle

B. when the angle of incidence is greater than the critical angle

Explanation:

As we know by law of refraction of light that

now here we know that total internal reflection only occurs when light travel from denser medium to rarer medium.

so here

now if angle is critical angle then at that point angle of refraction must be 90 degree

so if angle is more than critical angle then it will always follow the law of reflection so correct answer is

B. when the angle of incidence is greater than the critical angle

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.

it's when something is going so fast it makes a loud noise, breaking the sound barrier, for example: a jet makes a loud noise, not only cause of the jet but because they reached a point where they went so fast that you can year the noise from various parts, kinda like a police car, lets say the car was going   so fast that you hear the siren of the cop car right next to you, but the car is probably a mile a way, it's cos the siren was next to you a few seconds if you understand me