An electrical puzzle

[marconi]

Attached is a circuit. It was a course problem I recently was involved with through long-term mentoring of a junior, bright member of the EF.

I thought others might like some mental fun too.

1. How much power is dissipated in R2?

2. Which is true? Both batteries supply energy? Only one battery supplies energy?

E1 = 45V E2 = 30V. R1 = 1800R R2 = 2200R R3 = 2700R R4 = 3900R

Assume batteries have zero internal resistance and are rechargeable types. Assume all wires and connections have negligible resistance.

Hint: Mesh analysis of dc circuits but there other ways of tackling this problem.

 

[Julie.]

When I replaced my old Casio with a newer one I was really disappointed to see they revered the order of entry (oh-er matron!) as I was used to the older method when you used the function key to compute the action on the current display value.

Exactly!!!

Mine was/is a Casio, even the same model number, just a newer version.

I find it very difficult to use.

It used to be if you want the sine of 30 you entered 30 then sin, now you enter sin( then 30

The first is how my brain works, calculate the inner bit, then take the sine !

 

[Aaron b]

Balls... I was trying to work out R3! 69.13mW for that one.
That was good fun though, thanks.

 

[pc1966]

It used to be if you want the sine of 30 you entered 30 then sin, now you enter sin( then 30

The first is how my brain works, calculate the inner bit, then take the sine !

The older models worked very much like a CPU with the display as the accumulator register that stuff happened to/from.

Actually that is another thing to throw in to the discussion - doing such electrical circuit mesh analysis by hand is similar to assembly language programming. Anyone who writes software should be able to do it and understand it so they grasp the basics, but nobody in their right mind uses it for anything where it could be done in a higher level language.

 

[Julie.]

The older models worked very much like a CPU with the display as the accumulator register that stuff happened to/from.

Actually that is another thing to throw in to the discussion - doing such electrical circuit mesh analysis by hand is similar to assembly language programming. Anyone who writes software should be able to do it and understand it so they grasp the basics, but nobody in their right mind uses it for anything where it could be done in a higher level language.

I think a lot is to do with how we oldies think about maths.

If I am adding a list of say 10 numbers up, I do it in stages:
5+26= (31) +100= (131) +20= (331) ... Hang on, that's wrong... I must have done something wrong. So I start again getting a total for the 10 as say 606 - and am fairly assured the answer is correct.

Whereas today, people just punch the 10 numbers 5+26+100+20..... = 786 - It must be right I did it on a calculator.

Modern calculators suit this latter method.