Need Help Working Out This Question!

[Edwardioo]

The Following resistors are connected in series to a 240v supply, 10ohm, 20ohm, 30ohm, calculate to power dissipated in the 10ohm resistor.

How do i do this, and how would i do it for the 20ohm and the 30ohm resistor?

Cheers Ed.

 

[Adam W]

For resistors in series you simply add them together:

10 + 20 + 30 = 60Ω

P = V² ÷ R
P = 240² ÷ 60
P = 960W

 

[Edwardioo]

For resistors in series you simply add them together:

10 + 20 + 30 = 60Ω

P = V² ÷ R
P = 240² ÷ 60
P = 960W

your working out doesn't make any sense

 

[Adam W]

Bearing in mind [÷] should be the symbol for "divided by" which doesn't seem to work any more....
Which bit "doesn't make any sense "?

 

[telectrix]

total res. = 60ohms.

I = 230/60 = 3.83A

P = Isq xR

for 10ohm, P = 3.83 x 3.83 x 10 = 146.8watts

 

[mayfair]

bit techy for you init like

total res. = 60ohms.

I = 230/60 = 3.83A

P = Isq xR

for 10ohm, P = 3.83 x 3.83 x 10 = 146.8watts

 

[telectrix]

ain't had a beer yet mate. anyway it's basic secondary school ohms law.

 

[domino]

You should firstly always read the question carefully. It doesn't say whether it's an a.c. or d.c. supply. It just states a 240v supply.

The current in the circuit can be worked out from

I = V/R = 240/60 (total resistance in circuit) = 4A

To calculate the power dissipated in the 10 ohm resistor you first need to find the voltage across the resistor. Using Ohm's law again;

V = IR = 4*10 = 40V

Then using P = VI, P = 40*4 = 160W

 

[domino]

The thing to remember is that in a series circuit the current is the same throughout the circuit and the voltage is "shared out" between each component in the circuit.

It's the other way round for parallel circuits.

So for the 20 ohm resistor, we now know the current in the circuit is 4A, so we work out the voltage across the resistor again.

V = IR = 4 x 20 = 80V

Again P = VI = 80 x 4 = 320W

 

[telectrix]

my way is just as good, the only diff was i used 230v as could not see the question when i was typing the solution. and it don't matter if it's ac or dc as far as resistors are concerned.

 

[Adam W]

Hmm how was I so far out then?
I used one of the more obscure formulae off the formula wheel.
I never managed to get that thing to work.

OIC - didn't read the question properly.