GCE (A-level) Physics E19 Potential (Voltage) Dividers

Find out what a potential (voltage) divider is. Find out what the potential divider formula is, and how to use it to make (some) circuit calculation easier.

Category:

Education

Tags:

• GCE
• A-level
• AS
• A2
• Physics
• Potential
• Voltage
• Dividers
• divider
• formula

[headshotkillaz]

Hello I have a question about the question at 06:12.

I understand that we are working in Kiloohms.

When I was working it out, I worked out the current in the series first. Which is 1.06.

voltage in the 5kilo-ohm resistor.

= resistance x amperege.

What I'm asking is, why isnt the voltage 5333.34 volts, instead of 5.3.

Because although we are working in kiloohm. it just means we have 1000x of that many ohms. so 5kohm= 5000.

Shouldnt the answer be 5333.34 volts instead of 5.3 volts/5.3kilovolts

[Steve4Physics]

@headshotkillaz

Hi. The current is not 1.06A. I = V/R = 8/7500 = 1.067x10^-3A (= 1.067mA).

The voltage across the 5kohm resistor is then V = IR = 1.067x10^-3 x 5000 = 5.3V.

But if you use the potential divider formula, the 1000 cancels out top and bottom, so you can use units of kilohms in the formula.

Note, that with an 8V supply, you can never get voltages of more than 8V (unless you have some very complex electronics).

Hope that helps.



[Glennitub]

Hey, what if the resistor in parrallel does not have equal resistance to the resistor it is parrallel to? What happens to the overall resistance then?

Is it 1/Rt = 1/R1 + 1/R2?

[Steve4Physics]

@Glennitub

Here and example.

R1 (= 3Ω) and R2 (= 6Ω) in series connected to an 18V supply.

R1 has a pd of 6V and R2 has a pd of 12V. (Check it for yourself using the potential divider formula).

Add R3 (=4Ω) across R2. Together R2 and R3 make RT. 1/RT = 1/6 + 1/4. This gives RT = 2.4Ω. (Check it yourself.)

Now we have R1 in series with RT.

Pd across R1 = 18 x (3/(3+2.4) = 10V

Pd across RT = 18-10 = 8V

So R2 and R3 now both have a pd of 8V

(Total resistance reduced from 3+6 to 3+2.4)

[jptbaba]

@Steve4Physics So its the yields the same result by calculating the net resistance?

[Steve4Physics]

@jptbaba

Hi jptbaba. Yes, if you prefer, you can find the total resistance, then the current, and then find each resostor's voltage by using V = IR on each resistor separately. It must give the same answer as using the potential divider formula.

[Th3FinishingT0uch]

Thank you very much. Great video, well explained and great examples to compliment it. Great job.

[UtubeJKZ]

this made me realize a lot of things that i couldnt understand in my textbook. thanks for everything :D

[nodeal09]

This helped alot! Thank you very much!

[kristyLV]

it was very helpful thanks

[DevillYouth]

Thank you Steve. You've explained this in a way that my physics teacher couldn't. Please don't stop making these videos!

[YoungBazzy]

I have to say this was very nicely done and improved my understanding and will help in my A level physics

But if you have time i would really want some examples of potential divider circuits.

For example how does a potential divider circuit containing a thermistor do its job?

How does a potential divider circuit containing a LDR turn street lamps on and off?

I have problems understanding this when a variable resistor such as a thermistor/ldr is placed within the circuit