question 29

[hanggingou4315]

since the bubble is made of air and the light shines on it is from air, i assume that there's no change in medium. thus, i chose D instead of A. however, if i assume that the index of refraction at the surface of the bubble is greater than air then A makes sense.

[mcat_premed3832]

This almost begs the "philosophical" question (kidding!): what is the bubble??

But really, the bubble is of course air and its shape, a sphere, occurs in water because it is the shape that maximizes volume and minimizes surface area. The key point I'm making is that the sphere exists as is because of the interaction of 2 media: water and air. The problem must be solved by examining the frame of reference within the test tube, at the interface of these 2 media.

If a ball is thrown from a moving train by an twisting acrobat and the ball hits a box and the box moves, if the problem is about the box, then your frame of reference is just the box and you only deal with the force of the ball on the box, and depending on the angles, the force of friction if there is any. The stuff happening on the train is only relevant in terms of the interaction of the ball to the box in our frame of reference.