Little help if you can please.

[JAWS]

Apologies for asking probably simple questions to many of you & I spend quite a long time trying to work things out myself rather then asking for a quick fix but these are getting on my nerves as I can’t get my head around it.

Once I understand the working outs I seem to get on a roll for a while but seem to be struggling currently with these types of questions for some reason.

Thank you in advance for any help.

Q1...A current of 4.5 A flows in a 3.5 Ohm resistor for 5.5 minutes. The energy dissipated is.?



Q2...Calculate the current by a 100 Watt lamp having a working resistance of 200 Ohms.?



Q3...The power developod in resistor of 24 Ohm is 225 W. The Current Flowing is.?

 

[Bobster]

What have you worked out so far then?

What part of the question do you not understand?

 

[FatAlan]

Presumably you’ve been given the formulas that are used to work out the relationship between V I R & W?

 

[telectrix]

 

[JAWS]

Can get my head around basic OMS law V=IR & vice versa etc but when the question is there my mind freeze. I’ll just have to get back my head back in the book. Forgot about that wheel where you can convert them I’ll now take a good look at that.

Thanks

 

[JAWS]

Right I believe I have worked it out not sure if this correct.
A current of 4.5 A flows in a 3.5 Ohm resistor for 5.5 minutes. The energy dissipated is?

I’ve done 3.5x 3.5=12.25 x 4.5 = 55.125 x 5.5x60

=18191.25

 

[JAWS]

Just worked out the other answer too regarding current flowing using P=I2R answer 3.0618.

Hope these are correct

 

[Richard Burns]

Q1...A current of 4.5 A flows in a 3.5 Ohm resistor for 5.5 minutes. The energy dissipated is.?
In this question you have been given the current (I) and the resistance (R).
You have also been given the time of operation in minutes.
You have been asked for the energy dissipated.

Energy is in Joules and this is related to the usual values (PVIR) as Power (P) in Watts (which is joules per second).
Therefore initially you need to determine the power when you have I and R. Using the chart given by Tel, in the top left quadrant (for power) the equation is R * I².
Then you can calculate the power.
Then you multiply the power by the time in seconds and get the quantity of Joules, the energy dissipated.

For the answer you gave just check the selection of I (4.5A) and R (3.5Ω).


Q2...Calculate the current by a 100 Watt lamp having a working resistance of 200 Ohms.?
You have been given power in watts (P) and resistance in ohms (R).
You are asked to find the current flowing in amps (I).
From the bottom left quadrant (for I) of the disc the equation is
√(P/R) or you can consider it as I² = P/R.

Q3...The power developed in resistor of 24 Ohm is 225 W. The Current Flowing is?

You have been given resistance (R) and power (P) and you need to find Current (I).
This is the same as the previous question I²=P/R.
I² = 225/24 = 9.375
I = √9.375 = 3.06 A
As you have correctly calculated.

 

[JAWS]

Thank you Richard for taking the time out to explain that throughly.

I’ve been practicing the wheel this evening and slowly getting there.

Was that answer correct Richard 18.191.25J

 

[JAWS]

Can’t seem to work out my answer using R * I².

 

[Richard Burns]

You have R is 3.5Ω
You have I is 4.5A
P= I²R
I² is 4.5*4.5=20.25
R * 20.25 = 3.5 * 20.25 = 70.875 W (J/s)
Time is 5.5 minutes = 330s (I am assuming 5 1/2 minutes)
W * s = J
70.875 * 330 = 23.388 kJ

 

[Richard Burns]

In your first answer you were squaring the resistance not the current.

 

[JAWS]

Thank you Richard.