2330 level 2

[caff6363]

Hello, I have just started the 2330 level 2 and i have been given a question by my tutor that i cant get my head around. Question: Three 18 ohm resistors are connected in parallel across a 12 volt supply. The total power dissipation of the resistor load is: a) 3 Watts B) 18 Watts c) 24 Watts d) 36 Watts. When i work it out iam not getting any of these results could you show me how to calculate it. Thankyou. Also any help would be appreciated with the course. Cheers:_|

 

[Lurch]

How are you working it out?

There's 2 parts. Firstly work out the total resistance of the 3 parallel resistors and then using this you can do the second part and work out the power dissipated using the standard formula.

 

[caff6363]

no offence taken. I got my info from a book here we go i dont know whether iam doing it right. 1/Rt = 1/R1+1/R2+1/R3 = 1/Rt = 1/18 + 1/18 + 1/18 = 3+2+1 over 54, 1/Rt = 6/54

= Rt = 54/6 = 9 ohms= I= V/R = 12/9=1.333333333. This is the answer i get Please help. Thankyou

 

[androiduk2002]

I was taught a differant method of getting Rt but then again we was all told to buy a specific calculator Casio FX-83ES

Rt = (1)/(1/18+1/18+1/18) this works out to be 6ohms

V/Rt 12/6 = 2A

 

[caff6363]

thankyou for your reply but 2A is not one of the answers on the question sheet they are 3 watts, 18 watts, 24 watts and 36 watts it is supposed to be one of these unless it is a trick question i dont know

 

[androiduk2002]

Power (watts) = voltage (V) X Current (A)

 

[Megaohm7]

When you add your three 18 ohm resistances in parallel you get 6 ohms you divide this v = 12 / 6 to get 2amps then its p = 2*2*6=24 watts you have to square the current then times that by the resistance to give you the power

 

[androiduk2002]

When you add your three 18 ohm resistances in parallel you get 6 ohms you divide this v = 12 / 6 to get 2amps then its p = 2*2*6=24 watts you have to square the current then times that by the resistance to give you the power

slight differant method but still the same answer and I havent even covered this area yet ROTFWL but i found the answer in one of our recommened reading books

Electrical Installation Calculations

A.J. Watkins , C.Kitcher

 

[Bane]

Just been beaten to it!

Answer is C= 24 watts.

You have 3 resistors at 18 ohms each.

Find the common denominator (which again is 18).

18 into 18 = 1

So again you will have 1/18 + 1/18 + 1/18 = 3/18

Now invert it 18/3 = 6

Now apply ohms Law as we need to find Amps because then we can find Wattage by multiplying V x A

So, Volts = 12v

Resistance = 6 ohms

Volts divides by Resitance equals 2. Amps equals 2

ohms Law should now look like:

V=12

I =2

R=6

V x I = 24Watts

 

[Megaohm7]

Just been beaten to it!Answer is C= 24 watts.

You have 3 resistors at 18 ohms each.

Find the common denominator (which again is 18).

18 into 18 = 1

So again you will have 1/18 + 1/18 + 1/18 = 3/18

Now invert it 18/3 = 6

Now apply ohms Law as we need to find Amps because then we can find Wattage by multiplying V x A

So, Volts = 12v

Resistance = 6 ohms

Volts divides by Resitance equals 2. Amps equals 2

ohms Law should now look like:

V=12

I =2

R=6

V x I = 24Watts

slightly different method to me but same answer all the same

 

[androiduk2002]

Interesting to see the differant methods used , but they have all come to the same answer, so no right or wrong method, just what ever you are taught.