13.2 - more about resistance

rules for resistors in series

do resistors in series pass the same or different currents?

here

the same current

here

for resistors in series, current in = ?

current in = current out

current in = current out - true for resistors in series or parallel?

series

why do resistors in series pass the same current?

here

current rules for components in series - the current passing through two or more components in series is the same through each component

resistors pass the same current - is this true for resistors in series or parallel?

true for resistors in series

for resistors in series, the total pd = ?

the sum of the individual pds

here

why is the total pd of resistors in series the sum of the individual pds?

potential difference rules - for two or more components in series, the total pd across all the components = the sum of the potential differences across each component

here

the total pd is the sum of all the individual pds - is this true for components in series or parallel?

true for components in series

how do you notate resistors in parallel?

here

for two or more resistors in series, the total resistance = ?

total resistance = the sum of the individual resistances

the total resistance for two or more resistors = the sum of the individual resistances - is this true for resistors in series or parallel?

true for resistors in series

why, for two or more resistors in parallel, does the total resistance = the sum of all individual resistances?

here

for resistors in series, R_total = ?

R_total = R₁ + R₂ + R₃ + …

R_total = R₁ + R₂ + R₃ + … - true for resistors in series or parallel?

series

for resistors in series, V_total = ?

V_total = V₁ + V₂ + V₃ + …

V_total = V₁ + V₂ + V₃ + … - true for resistors in series or parallel?

series

rules for resistors in parallel

for resistors in parallel, what is the pd of each resistor?

they have the same pd

why do resistors in parallel have the same pd?

according to potential different rules - pd across components in parallel is the same (further explanation in 13.1 q56)

for resistors in parallel, V_total = ?

V_total = V₁ = V₂ = V₃ = …

V_total = V₁ = V₂ = V₃ = … - true for resistors in series or parallel?

parallel

for resistors in parallel, I_total = ?

I_total = I₁ + I₂ + I₃ + …

I_total = I₁ + I₂ + I₃ + … - true for resistors in series or parallel?

parallel

what do you have to consider when finding the total resistance of resistors in parallel?

• 1 / R_total = 1 / R₁ + 1 / R₂ + 1 / R₃ + … ,

• calculate 1 / R_total using the equation

• ( 1 / 1/R_total) = R_total

how else can you calculate the resistance of two resistors in parallel?

the resistance of two resistors in parallel = their product / their sum

here

what is the heating effect of an electric current in any component due to?

the resistance of the component

how does the resistance of a component cause a heating effect of an electric current in any component?

• charge carriers repeatedly collide with positive ions of the conducting material

• there is a net transfer of energy from the charge carriers to the positive ions as a result of these collisions

• after a charge carrier loses kinetic energy in such a collision, the force due to the pd across the material accelerates it until it collides with another positive ion

in a heating effect, what particles are colliding?

charge carriers are colliding with positive ions of the conducting material and each other

in a heating effect, what is a consequence of the collisions?

there’s a net transfer of energy from the charge carriers to the positive ions, meaning a charge carrier loses its kinetic energy

in a heating effect, what causes a charge carrier to lose kinetic energy?

the net transfer of energy from the charge carrier to the positive ion of the conducting material the charge carrier is colliding with

in a heating effect, what happens after a charge carrier loses kinetic energy?

the force due to the pd across the material accelerates the charge carrier until it collides with another positive ion

in a heating effect, can a charge carrier loses its kinetic energy by colliding with another charge carrier?

maybe but i don’t think so. it transfers its energy to a fixed positive ion in the conduction metal, so it can only lose its kinetic energy when colliding with a positive ion

where is the heating element on a kettle?

here

where is the heating element on an iron?

here

what is a heating element?

rate of heat transfer = ?

rate of heat transfer = I²R

derive this equation - rate of heat transfer = I²R

here

if a component heats up, what does its temperature rise depend on?

• the power supplied to it (I²R)

• the rate of heat transfer to the surroundings

what does the power supplied to a component affect?

the temperature rise of the component, if the component heats up

what does the rate of heat transfer to the surroundings from a component affect?

the temperature rise of the component, if the component heats up

where does the power supplied to a heating element come from?

electrical energy from the mains

what is the energy transfer in a heating element?

electrical energy from the mains → thermal energy

what is the energy transferred to a heating component by an electric current?

energy transferred = power x time = I²Rt

energy transferred = power x time = I²Rt

the energy transferred to a heating component by an electric current

what is the energy transferred per second to the component?

the power supplied to the component

does the energy transferred per second to the component depend on current direction?

no

what doesn’t current direction affect?

the energy transferred per second to the component