Potential Dividers - A Level Physics Exam Practice Question - Calculation Question

[@jfernandes_25]

Hi sir, I was wondering where to get resources for exam questions as physics maths tutor has them split on topics which is good but I've done lots of them and I haven't done most of the content for a full exam, Thank you

[@KitBetts-Masters]

Hiya, your teachers will probably have something like exam pro / test base etc where they canake bumper packs of exam questions for you. Or otherwise check out Isaac physics as it's the best practice. My top grade students swear by it!

[@jfernandes_25]

@@KitBetts-Masters Thank you so much Sir👍your the best

[@georgeacres4]

For the first part to the question, how can n increase? I thought n is different for each material, but the same material will always have the same, constant value of n. Also, how do you know that the resistance would therefore decrease? Thanks!

[@KitBetts-Masters]

George Acres it is the same for each material. but for semi conductors it can change given certain conditions, e.g. light or temp. in thermistors heat energy allows some extra electrons to become "free" therefore there's more of them available to carry current, therefore lower resistance. good question! :-)

[@georgeacres4]

When the heat energy allows more electrons to become "free", where do these electrons come from? And I get that electrons carry the charge around the circuit. How would there being more electrons available, how would that lower the resistance? I know that resistance is how difficult it is for the current to flow (as the electrons collide with lattice ions), but how would having more available electrons lower the resistance? I don't get that, please could you explain? Thank you :)

[@KitBetts-Masters]

So these electrons come from the atoms. Think quantum, the extra energy promotes them up the energy levels until they are in the valence band, "free electrons". To get this you'll need to think about resistance slightly differently. If you define resistance as inhibition of current (or =R=V/I), and current as a rate of flow of charge, i.e. I=Q/t then it makes more sense that having more charge available (Q) effectively decreases the resistance. This is a good example of when it is better to define a quantity by its quantitative relationship to other quantities is more useful than to spend a lot of time thinking about the qualitative aspects of it. These are important but, the algebra helps us to understand what is going on in these counter intuitive phenomena. I hope that all makes sense. K

[@georgeacres4]

GorillaPhysics Thanks. When you have a really simple circuit (like a light bulb in a school experiment) and we use a power supply, why do we actually need to use that power supply? Is it to reduce the voltage/current? If so, does it reduce the voltage, the current, or both?

[@KitBetts-Masters]

So that's called a low voltage supply. It has a wopping great potential divider in it, and so we can divide off 0-12V of the mains supply. It also has a circuit breaker in it which limits the current to 8.5A (usually) this is one of the safety features.

[@fredy749]

Good morning Sir. Why all video on youtube are very allergic talking about the hard part of past papers? For example, I cannot find anywhere the solution of 9702 a level physics Paper 4 2007 N.6?

[@KitBetts-Masters]

Not allergic at all... In fact sent through hardest questions live two years ago: kzbin.info/www/bejne/Y2GUhZuOe7mUg6M

[@fredy749]

@@KitBetts-Masters Oh, okay. I am looking for CIE but unfortunately this is AQA.