The student was looking at two simple circuits. The first had a 100Volt battery

Question

The student was looking at two simple circuits. The first had a 100Volt battery hooked across a 20 Ohm resistor. The second took thatsame battery, unhooked it from the 20 Ohm resistor and hooked it upto a 4 Ohm resistor.

He thought to himself, "OK, 100 divided by 20 is 5...so that meansthis battery puts out 5 Amps of current. When I hook that batteryup to the 4 Ohm resistor, the 5 Amps that flow through it wouldgive a potential difference of 5 times 4...20 Volts. Wait, 20doesn't equal 100. Uh-oh."

Your job here is to clear up the student's confusion. Our studentis pretty good at math...he's perfectly aware that 100 Voltsdivided by 4 Ohms gives 25 Amps. The issue is how he's thinkingabout the battery. What is he assuming a battery does? What does abattery really do (i.e. what does a battery really provide for thecircuit?)

Explanation / Answer

   Battery is to be taken as a constant voltagesource as long as its internal resistance is much lower than theexternal resistance. Hence he should use EMF of battery as aconstant value.

Related Questions

Navigate

• Browse (All)
• Browse T
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.