The document discusses electromotive force (EMF) and how it relates to voltage, work, and current flow in a circuit. It explains that a battery or generator produces a voltage difference across its terminals by converting chemical or mechanical energy into electrical energy. When a resistor is connected across the battery terminals, charge carriers flow through the circuit as current. The ability of the battery to move these charge carriers is measured by its voltage and represents the work done per unit charge by the EMF source. Voltage is distributed among and dropped across the different components in a circuit based on the amount of current and resistance.

1. EMF
• A current is maintained in a closed circuit by a source of em
Among such sources
• are any devices such as batteries (see Fig. 18.1) and
generators that increase the potential energy of the
circulating charges. A source of emf can be thought of as
• a “charge pump” that forces electrons to move in a direction
opposite the elec_x0002_trostatic field inside the source.
The emf e of a source is the work done per unit charge; hence,
the SI unit of emf is the volt.

2. ELECTROMOTIVE FORCE (EMF)

3. EMF

4. EMF.......CONTINUED

5. EMF.......CONTINUED

6. EMF.......CONTINUED

7. EMF.......CONTINUED

8. EMF.......CONTINUED

9. • Voltage, Work, and Current Flow
• A battery converts chemical energy into electrical energy,
producing a voltage—i.e., a difference in electric
potential—across its two terminals. A resistor is a
component that creates a specified amount of resistance
to electric current. When we connect the two terminals of
a resistor to the two terminals of a battery, charge carriers
move through the circuit, and we call this electric current.
EMF.......CONTINUED

10. • Voltage conveys the ability to do the work of moving charge from one
point to another. A 5 V battery, for example, can do 5 joules of work per
coulomb of charge. When current is flowing through a resistor, we can
measure the amount of work (per unit charge) required to keep the
current flowing through the resistor.
• This is the essence of voltage drop: a battery (or voltage source)
supplies energy for doing the work of moving charge. When current is
flowing, components such as resistors consume energy, and the
amount of work per unit charge associated with the current flowing
through a given component is the component’s voltage drop.
EMF.......CONTINUED

11. • The voltage dropped by a component accounts for a
portion of the voltage generated by the battery. In other
words, the work performed by the battery is divided up
among the components in the circuit.
• We can intuitively recognize that driving a given amount
of current through more resistance will require more work.
Thus, if two resistors are in series (meaning that they
have the same current flow), the resistor with more
resistance has a larger voltage drop. This is the basis for
the operation of the voltage divider circuit.
EMF.......CONTINUED

12. EMF.......CONTINUED