EasyPhysicsHigh School (11–12)Electricity & Magnetism › Current ElectricityNumericalBoard ExamAPA-LevelIB
Currents of 2.4 A and 3.1 A flow into a junction.
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Currents of and flow into a junction. Three wires take current out: two carry and . What does the third carry, and which way?
Need a reminder? The key ideaShow
Junction rule: the current in equals the current out (charge is conserved). Loop rule: round any closed loop the changes of potential add to zero (energy is conserved): across a cell from to , across a resistor along the current. A negative answer means the current flows the other way.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. In. .
Step 2. Out so far. .
Step 3. The third wire. , out of the junction.
Answer: , flowing out.
Check. , the current in.
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