4.2.1.3 Current, Resistance and Potential Difference Flashcards
What does current through a component depend on?
The current (I) through a component depends on both the resistance (R) and the potential difference (V) across the component
the greater the resistance…..
the greater the resistance of the component the smaller the current for a given potential difference (pd) across the component as the rate of flow of charge decreases (as charges have more to travel through)
What does electric potential measure?
Measures the amount of energy per unit of charge
What is electric potential measured in?
Volts (V)
What is 1V equivalent to?
1V is equivalent to 1J per coulomb
What does potential difference measure?
potential difference measures the amount of energy transferred per unit/coulomb of charge
What is p.d. measured in?
Volts (V)
What is a p.d. of 1V is equivalent to?
a p.d. of 1V is equivalent to 1 Coulomb of charge losing or gaining 1J of energy
How is p.d. measured?
p.d. is measured with a voltmeter, which is connected in parallel, across component(s)
How can you work out p.d.?
to work out potential difference use colouring pens method - change pen colour every time you reach a new component
What is the electric potential of the negative side of the cell always?
the negative side of the cell is always 0V
When does the energy per charge change?
the energy per charge only changes when going through components
What happens when you add bulbs to a circuit
when you add bulbs to a circuit in series you add resistance, the resistance increases and the current (rate of flow of charge) reading on the ammeter decreases
What happens when wire is added to a circuit?
- when the length of a wire in a circuit increases the current decreases as the resistance increases
- current decreases in similar increments when the same amount of wire is added
What happens when you add cells to a circuit?
- the potential difference increases so there is more energy (as long as cells are going correct way), more energy reaches the bulb at a certain point
- the current increases so rate of flow of charges increases and energy reaches bulb faster
- increasing the p.d. increases the current whilst also increasing the resistance which decreases the current
How do you make bulbs brighter?
- increase current = brighter bulb(s) as E in charges reach bulb faster as rate of flow of charge is faster so there is a greater power output/higher E output per second
- increase in potential difference = brighter bulbs as charges have more energy
Increasing the potential difference….
- increases the current
- decreases the current as the resistance would have to increase to increase the potential difference which would decrease the current
Why do bulbs become dimmer when you add more bulbs?
- potential decreases - E has to be shared between the bulbs
- the resistance increases so the current decreases - rate of flow charge decreases
What happens as electrons flow through a conductor?
- As electrons flow through a conductor they collide with metal ions
- flow of current is being resisted
- resistance of current is measured in ohms
How does increasing potential difference effect current?
- current flowing through component determined by the potential difference across the component and the resistance of the component
- increasing the p.d. increases the current whilst also increasing the resistance which decreases the current
Formula to calculate potential difference:
What affects current?
- current
- depends on what is in a circuit - not fixed
- potential difference
- number of cells per energy
- increase in V —> increase in I
Resistance:
- hindrance/opposition to the flow of charge - any extra components cause current to decrease
- R = V/I
Units of resistance:
ohms Ω
How can the increase of potential difference across a bulb cause a decrease in current?
- metals contain free electrons which carry charge
- as p.d. increases the current to increase
- this means the current has a greater heating effect so the metal component increases in temperature causing metals ions in the filament to move faster
- causes an increase in frequency of collisions of electrons with metals ions causing flow of electrons to slow down this causes resistance to increase
- causes rates of flow of charge (electrons) to decreases so current decreases
If a switch is added in parallel to a variable resistor in a circuit what happens to the current going through the variable resistor and why?
- current would be almost 0 in variable resistance
- as switch had almost no resistance
