A difficult circuit problem

[Histones to DNA]

Hello everyone.

 

 

I have an urgent electricity question which can be viewed in the attachment.

 

The question is: Calculate

 

a)the current in the main circuit

 

b)the p.d. across the 4 ohms resistor

 

c)the current through the 12 ohms resistor

 

For part a), What I did to find the total resistance is to find the resistance of the resistors connected in parallel first. So 1/R = 1/4 + 1/12 gives 3 ohms.

Then I would add 3 ohms with 7 ohms, which would be equal to 10 ohms - that is the total resistance of the circuit. Now I have to apply Ohm's law - I = V/RI = 20V/10R =2A

 

Can anyone please help me in part b and c? Thank you so much!

Edited September 27, 2010 by Histones to DNA

[Danijel Gorupec]

You started right!

 

Notice:

a) the voltage drop on the 4ohm ressistor is the same as voltage drop on the 12ohm resistor (these two are in parallel)

B) voltage drop on the 4ohm ressistor (or 12ohm resistor) plus voltage drop on the 7ohm resistor equals to 20V

c) current through 4 ohm resistor + current through 12 ohm resistor equals to 2A

d) power dissipation can be calculated: P=voltage * current

 

The Ohm's law you already know