Suppose a special kind of glass has a refractive index which decreases from 2.4 to 2.0 when heated above 50°C. By how much does the critical angle of this glass increase when heated? Give your answer in degrees, without a unit and to two significant figures.

think its the third option

wire in brush may conduct electricity from cell to drill and vice versa electrc shock possible

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