How Do You Calculate EMF and Internal Resistance in a DC Circuit?

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In summary, to find the emf and internal resistance of an unmarked battery, you are given two resistors of value 5.0(ohms) and an ammeter. When the resistors are connected in parallel, the current drawn from the battery is 2.0A. By using the equations E = IR and E = IR + Ir, the internal resistance of the battery is found to be 2(ohms) and the emf is found to be 9V.
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natural
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Homework Statement


To find the emf and internal resistance of an unmarked battery you are given two resistor of value 5.0(ohms) and an ammeter. When the resistors are connected in parallel the current drawn from the battery is 2.0A. What are the e.m.f and internal resistance of the battery?

Am i going right?

Homework Equations


E = IR = Ir

The Attempt at a Solution


Series
R = 5(ohms) + 5(ohms) = 10(ohms)

Parellel
1/R = 1/5 + 1/5 = 2/5
R = 2.5(ohms)

E = 0.75*10 + o.75*r
E = 7.5 + 0.75r ------- (1)

E = 2*2.5 + 2r
E = 5 + 2r ---------- (2)

7.5 + 0.75r = 5 +2r
2.5 = 1.25r
2(ohms) = r

there for r in equation 1 gives
E = 7.5 + 0.75(2)
= 9V
 
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  • #2
***TYPO****-*********Relavant Equation should be E = IR + Ir*******
 
  • #3
You didn't include the series combination part in your problem statement. But looking at your work, it would appear that you get 750mA when you connect them in series?

If so, then the rest looks correct.
 

1. What is a D.C circuit?

A D.C circuit, or direct current circuit, is a closed loop of conductive material through which electric current flows in one direction only.

2. How does a D.C circuit differ from an A.C circuit?

In a D.C circuit, the current flows in one direction only, while in an A.C circuit, the current periodically changes direction.

3. What are the basic components of a D.C circuit?

The basic components of a D.C circuit include a power source (such as a battery), conductors (wires), and various components such as resistors, capacitors, and switches.

4. How do I calculate the current, voltage, and resistance in a D.C circuit?

The current (I) can be calculated using Ohm's Law (I = V/R), where V is the voltage and R is the resistance. The voltage (V) can be calculated by multiplying the current by the resistance (V = I*R). The resistance (R) can be calculated by dividing the voltage by the current (R = V/I).

5. How does Kirchhoff's Laws apply to D.C circuits?

Kirchhoff's Laws, specifically Kirchhoff's Current Law and Kirchhoff's Voltage Law, are fundamental principles that govern the behavior of D.C circuits. They state that the sum of currents entering a node must equal the sum of currents leaving a node, and the sum of voltage drops in a closed loop must equal the sum of voltage sources in that loop.

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