Hello! I've been doing some questions of BOSTES and I came across these questions. Help would be greatly appreciated
Hey! For the first one, we know a current will flow, and since the relative motion of the disc and the magnetic field is always the same, it will be a
direct current, so we can cut out two answers straight away! By the right hand slap rule, the current induced will move towards Brush Y (remember fingers in direction of field, thumb in direction of movement, slap in direction of current - So I'm
fairly sure the answer C?
Second one, we know the induced emf will be a maximum when the coil is parallel to the field, so we need to start at a peak value. There is one full rotation, so one complete oscillation. This matches Graph B!
This is a really tough one to explain online, but it again relies on right hand grip rule. Remember first that the force on a charged particle due to movement in a magnetic field is perpendicular to both the field AND the movement. So if we want it to experience a force in the same direction as current, it can't be moving in that direction initially. So that rules out A and B.
So if current goes upwards (let's say), that means the field will be into or out of the page around it. To get a force in the same direction as the current, we need it to be moving towards it to get an upwards force. In honesty, I'm thinking of ways to explain this, but I really can't without being there next to you showing it to you in real time, aha. Try it - Try the right hand slap rule and see what happens when the electron is moving towards the wire - It should all line up to give you a force in the same direction as the current