4.2.1.3 Current, Resistance and Potential Difference

Question 1

What does current through a component depend on?

Answer 1

The current (I) through a component depends on both the resistance (R) and the potential difference (V) across the component

Question 2

the greater the resistance…..

Answer 2

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)

Question 3

What does electric potential measure?

Answer 3

Measures the amount of energy per unit of charge

Question 4

What is electric potential measured in?

Answer 4

Volts (V)

Question 5

What is 1V equivalent to?

Answer 5

1V is equivalent to 1J per coulomb

Question 6

What does potential difference measure?

Answer 6

potential difference measures the amount of energy transferred per unit/coulomb of charge

Question 7

What is p.d. measured in?

Answer 7

Volts (V)

Question 8

What is a p.d. of 1V is equivalent to?

Answer 8

a p.d. of 1V is equivalent to 1 Coulomb of charge losing or gaining 1J of energy

Question 9

How is p.d. measured?

Answer 9

p.d. is measured with a voltmeter, which is connected in parallel, across component(s)

Question 10

How can you work out p.d.?

Answer 10

to work out potential difference use colouring pens method - change pen colour every time you reach a new component

Question 11

What is the electric potential of the negative side of the cell always?

Answer 11

the negative side of the cell is always 0V

Question 12

When does the energy per charge change?

Answer 12

the energy per charge only changes when going through components

Question 13

What happens when you add bulbs to a circuit

Answer 13

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

Question 14

What happens when wire is added to a circuit?

Answer 14

• 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

Question 15

What happens when you add cells to a circuit?

Answer 15

• 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

Question 16

How do you make bulbs brighter?

Answer 16

• 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

Question 17

Increasing the potential difference….

Answer 17

• increases the current
• decreases the current as the resistance would have to increase to increase the potential difference which would decrease the current

Question 18

Why do bulbs become dimmer when you add more bulbs?

Answer 18

• potential decreases - E has to be shared between the bulbs
• the resistance increases so the current decreases - rate of flow charge decreases

Question 19

What happens as electrons flow through a conductor?

Answer 19

• As electrons flow through a conductor they collide with metal ions
• flow of current is being resisted
• resistance of current is measured in ohms

Question 20

How does increasing potential difference effect current?

Answer 20

• 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

Question 21

Formula to calculate potential difference:

Answer 21

Question 22

What affects current?

Answer 22

• current
  
  • depends on what is in a circuit - not fixed
• potential difference
  
  • number of cells per energy
  • increase in V —> increase in I

Question 23

Resistance:

Answer 23

• hindrance/opposition to the flow of charge - any extra components cause current to decrease
• R = V/I

Question 24

Units of resistance:

Answer 24

ohms Ω

Question 25

How can the increase of potential difference across a bulb cause a decrease in current?

Answer 25

• 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

Question 26

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?

Answer 26

• current would be almost 0 in variable resistance
• as switch had almost no resistance