Physics problem (electric circuits)

[roelj]

When practising for an exam I came across the following problem. I thought it was simple, yet I cannot find the solution.

Could anyone help me and show how this problem can be solved?
I attached an image of the question.

Many thanks in advance because it drives me crazy.

[roelj]

I think the resistance of the light bulb should be about 20 times as big as the 10 Ohms resistor.

[stevea]

Rb = light bulb impedance
Ib =  current thru bulb                Ib    = 0.010 ampere
Rp = impedence of bulb || 10 ohm
                                       Rp   = (Rb*10 ohm)/(Rb+10 ohm)
Impedence on the battery is 	       RL   = 20 ohm + Rp + 20 ohm = Rp 40 ohm
Current form battery is                Ibatt = 10v / RL = 10v / ( Rp + 40 ohm )
Voltage across the bulb is 	       Vb   = Ibatt * Rp

                                       Rb   = Vb / Ib [definition]

The rest is just algebra

Rb = 192 ohm

[roelj]

Thanks stevea!

[beaker_]

Funny, I figured ~92 Ohms but I'm using a pencil just blowing through it (no calc).


Solve it by redrawing it, label everything and all you need to know is:
Sum the V around the loop = 0
Sum of the I at any node = 0
After that it's Ohms's law.

Good luck.


Late Edit: Oops... I used 20mA through the branch.