urgent help needed phyiscs unit 2!

[JustAnotherPerson22]

Hi, title says it all
I really need help with january 2009 question 16a, b
how can lamp A have less resistance but glow dimmer?

 

[alex]

I didnt read the question, but when you talk about brightness, always check the power (VI, I^2R, V^2/R) and not the resistance alone

 

[jtbteddy]

V=IR, current across both of them is the same because they are in series. Voltage across lamp B is greater than that across lamp A.
V=IR, if I is same in both, V and R are directly proportional, and V is greater in lamp B, so R must also be greater. The opposite must happen for lamp A, get it?

 

[jtbteddy]

For part b, since they're in parallel, both lamps have the same voltage across them. You know from part a that the resistance across lamp A will be less than the resistance across lamp B. P=V^2/R. Power and resistance are inversely proportional to each other, therefore, the voltage across both is the same, but lamp A's resistance is lower, so the power of lamp A is greater, and it's brighter. The opposite occurs for lamp B