In this lesson, we will learn:

- How to compare and contrast the circuits we’ve been drawing so far (an ideal circuit) with a more realistic circuit (containing an EMF as well as internal resistance).
- What is EMF (Electromotive Force)? And what is terminal voltage?
- How to solve for terminal voltage and EMF using 2 methods:
- The traditional formulas for Ohm’s Law ($V=IR$ ) and terminal voltage formula ($V_{term} = \epsilon- Ir$ )
- Conceptual understanding and voltage divider formula ( $V_{x} = V_{total} \, \cdot \, \frac{R_{x} } {R_{total} }$ )

__Notes:__- To represent a more realistic electric circuit, a
actually contains__battery__—in other words, the battery itself uses up some of the voltage that it provides to the whole circuit.__internal resistance__ - Internal resistance is unavoidable because any material has some resistance
- Metals have a very low (but not zero) resistance and are good conductors for electricity; the greater the resistance of a material, the worse its conductivity
stands for__EMF__. It is a device that__Electromotive Force__**transforms**one type of energy into electrical energy. (i.e. An alkaline battery undergoes redox reactions whereby chemical energy is transformed into electrical energy to power the circuit).- A
is considered a source of electromotive force. A battery is actually composed of an__battery__($\epsilon$) and an__EMF__($R_{int}$ or $r$ ) connected in series.__internal resistor__ ($V_{term}$) is the voltage (__Terminal Voltage____potential difference__) measured between the terminals (positive and negative terminals) of a battery.- When
**no current**is flowing through the circuit:__emf = terminal voltage__ - When
**there is current**flowing through the circuit:__emf > terminal voltage__ - The general formula for the
is given as:__Terminal Voltage__ - $V_{term} = \epsilon- Ir$
- Where:
- $V_{term}$ is the voltage between the terminals of the battery (in volts, V)
- $\epsilon$ is the EMF of the battery; total/maximum voltage (in volts, V)
- $I$ is the total current flowing through the circuit (in amperes, A)
- $r$ is the internal resistance within the battery (in Ohms; $\Omega$)
- $Ir$ is actually the voltage drop across the internal resistor ($V = IR$), thus the formula can be adjusted: $V_{term} = \epsilon - V_{r}$
- Furthermore, the
represents the amount of electric potential energy (voltage) that is available to the circuit outside of (external to) the battery itself. Thus:__terminal voltage__ - $V_{term} = V_{used \, up} = V_{external}$
- And the $V_{total}$ or $\epsilon = V_{internal \, resistor} = V_{external \, resistor(s)}$
- To modify the
to be used with EMF and terminal voltage questions, we can solve for the total external voltage drop:__voltage divider general formula__ - $V_{term} = V_{ext} = \epsilon \, \cdot \, \frac{R_{ext} } {R_{total} }$