Current,Circuit Components, Series, Parallel Circuits,Resistance

How do we work out charge using current and time ?

charge = current x time

Q = I x t

What is current measured in ?

Amperes

What is the unit for charge ?

coulomb

How do we work out potential difference with current and resistance ?

potential difference = current x resistance

V = I x R

What is potential difference is measured ?

volts

What is resistance measured in ?

Ohms

True or False ? ‘The resistance of the lamp is directly proportional to the potential difference’

False - resistance increases with potential difference but doubling the potential difference does not result in doubling the resistance

A student used a power supply that had a fixed voltage. Each of these outputs was a whole number of volts ?

How could a student possibly add a component to a circuit that would provide a continuously variable voltage across the lamp ?

They could add a variable resistor in series with the lamp/power supply

OR

add a potential divider in parallel with power supply

True or False ? ‘As the potential difference across the lamp increases, the current in the lamp increases and the relationship is directly proportional’

False - current increases with the potential difference until it reaches a constant value. The current is not directly proportional to potential difference.

Explain why the resistance of a filament lamp changes as the voltage across it increases ?

As the resistance increases, the filament is being heated up so due to more collisions of electrons so the temperature also increases

A resistor is connected to a power supply. The resistor becomes warm while there is current in it.

Why does the resistor become warm ?

Due to the collisions between electrons and lattice and the lattice vibrates more

What way should ammeters and voltmeter be connected with a component in a circuit ?

ammeter in series with component, voltmeter in parallel

6 MARKER :

With a circuit diagram, explain a method a student could use to investigate how the resistance of a single lamp changes with the potential difference across the lamp ?

Circuit diagram should include:

• power supply

• ammeter

• voltmeter

• filament lamp

• means of varying potential difference

Method:

• measure the current with ammeter

• measure potential difference with voltmeter

• vary the potential difference

• calculate the resistance

• rep eat and compare

Why are wires to the battery in a car thicker than wires that connect each decide to its switch and its fuse ?

Thicker wires have low resistance and so less thermal energy is transferred in the wires - (wires don’t her hot), less potential difference/ voltage across the wires (more current can be carried)