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# physics - current and voltage watch

1. currently revising for a test
came across this question:
The current in a metallic conductor increases when the potential difference across it is increased. which of the following best explains this?
A there is less chance of a charge carrier striking an atom

B the mean time between collisions decreases

C the acceleration of charge carriers between collisions increases

D the rise in temperature increases the thermal motion of the charge carriers.

no idea which one is correct any help is appreciated
2. (Original post by trebor00)
currently revising for a test
came across this question:
The current in a metallic conductor increases when the potential difference across it is increased. which of the following best explains this?
A there is less chance of a charge carrier striking an atom

B the mean time between collisions decreases

C the acceleration of charge carriers between collisions increases

D the rise in temperature increases the thermal motion of the charge carriers.

no idea which one is correct any help is appreciated
These type of questions require an element of elimination and analysis and on inspection it is resolved by the effect on electron drift velocity as the voltage potential increases:

D) can be eliminated since temperature is a function of the rate of collisions and deflections between migrating electrons and ions in the lattice. It is an effect of increased current not a cause.

A) can be eliminated because as the amount of charge flowing increases, the probability of a charge carrier striking an atom must increase. Again, this is an effect of increased current and not a cause.

B) is incorrect since if the mean time between collisions decreases, then the rate of collisions has increased. i.e. again this is an effect not a cause of increasing current.

C) We know that an applied potential will cause electrons to drift towards the anode end of the conductor.

Collision with an ion doesn't necessarily stop an electron, it may also deflect in some random direction, after which the electron is again accelerated in the field direction.

Voltage potential is defined as the energy (Joules) available per Coulomb of charge.

Increasing the electric field increases the average acceleration of each electron.

Current is defined as the rate of change of charge and hence increased drift velocity. Hence Increasing potential causes an increase in the current.

C) is correct.
3. thanks I understand it now
4. In a circuit diagram if the ends of a battery reads +5V and -5V then is the overall voltage across the circuit 10V or 5V?
5. (Original post by Galibmehedijami)
In a circuit diagram if the ends of a battery reads +5V and -5V then is the overall voltage across the circuit 10V or 5V?
Potential Difference is just that: the difference between two voltage potentials in a circuit between which current can flow.

The potential difference between -5V and +5V is:

+5V - (-5V) = +5 + 5 = 10V
6. (Original post by Galibmehedijami)
In a circuit diagram if the ends of a battery reads +5V and -5V then is the overall voltage across the circuit 10V or 5V?
You're best off starting a new thread for a new question...

That sort of power supply is common in amplifier circuits but you might see it in other places - it's often called a split-rail supply (the power supply conductors are called rails)

the PD between -5V and +5 is 10V
if it was in an amplifier the output could be between +5 and -5V
quite often it'd be signal centred on 0V with an amplitude of 5V
7. Thanks. I get it now

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