Subject:

- 10.2: Electromotive Force
- Voltage, Current, and Resistance
- Chapter 2 - Ohm's Law
- FHSST Physics/Electricity/How Voltage, Current, and Resistance Relate
- Contributors
- Navigation menu
- Current resistance and electromotive force pdf creator
- Ohm’s Law - How Voltage, Current, and Resistance Relate
- EMF & Internal Resistance - A-level Physics
- Ohm’s Law - How Voltage, Current, and Resistance Relate
- Resisitors in Series

## 10.2: Electromotive Force

What drives current? We can think of various devices—such as batteries, generators, wall outlets, and so on—which are necessary to maintain a current. All such devices create a potential difference and are loosely referred to as voltage sources. When a voltage source is connected to a conductor, it applies a potential difference that creates an electric field.

## Voltage, Current, and Resistance

The electric field in turn exerts force on charges, causing current. The current that flows through most substances is directly proportional to the voltage applied to it.

The German physicist Georg Simon Ohm — was the first to demonstrate experimentally that the current in a metal wire is directly proportional to the voltage applied :.

It can be viewed as a cause-and-effect relationship, with voltage the cause and current the effect.

This is an empirical law like that for friction—an experimentally observed phenomenon. If voltage drives current, what impedes it?

## Chapter 2 - Ohm's Law

The electric property that impedes current crudely similar to friction and air resistance is called resistance. Collisions of moving charges with atoms and molecules in a substance transfer energy to the substance and limit current. Resistance is defined as inversely proportional to current, or.

Thus, for example, current is cut in half if resistance doubles. Combining the relationships of current to voltage and current to resistance gives. These include good conductors like copper and aluminum, and some poor conductors under certain circumstances.

## FHSST Physics/Electricity/How Voltage, Current, and Resistance Relate

Ohmic materials have a resistance that is independent of voltage and current. An object that has simple resistance is called a resistor , even if its resistance is small.

The unit for resistance is an ohm and is given the symbol upper case Greek omega. A simple circuit has a single voltage source and a single resistor.

The wires connecting the voltage source to the resistor can be assumed to have negligible resistance, or their resistance can be included in. Calculating Resistance: An Automobile Headlight What is the resistance of an automobile headlight through which 2. Rearranging and substituting known values gives. This is a relatively small resistance, but it is larger than the cold resistance of the headlight.

As we shall see in Resistance and Resistivity , resistance usually increases with temperature, and so the bulb has a lower resistance when it is first switched on and will draw considerably more current during its brief warm-up period.

## Contributors

Resistances range over many orders of magnitude. Some ceramic insulators, such as those used to support power lines, have resistances of or more. A dry person may have a hand-to-foot resistance of , whereas the resistance of the human heart is about.

A meter-long piece of large-diameter copper wire may have a resistance of , and superconductors have no resistance at all they are non-ohmic. Resistance is related to the shape of an object and the material of which it is composed, as will be seen in Resistance and Resistivity.

## Navigation menu

Additional insight is gained by solving for yielding. This expression for can be interpreted as the voltage drop across a resistor produced by the flow of current. The phrase drop is often used for this voltage. For instance, the headlight in [link] has an drop of If voltage is measured at various points in a circuit, it will be seen to increase at the voltage source and decrease at the resistor. Voltage is similar to fluid pressure. The voltage source is like a pump, creating a pressure difference, causing current—the flow of charge.

The resistor is like a pipe that reduces pressure and limits flow because of its resistance.

Conservation of energy has important consequences here. The voltage source supplies energy causing an electric field and a current , and the resistor converts it to another form such as thermal energy. In a simple circuit one with a single simple resistor , the voltage supplied by the source equals the voltage drop across the resistor, since , and the same flows through each.

Thus the energy supplied by the voltage source and the energy converted by the resistor are equal.

## Current resistance and electromotive force pdf creator

See [link]. Making Connections: Conservation of Energy In a simple electrical circuit, the sole resistor converts energy supplied by the source into another form. Conservation of energy is evidenced here by the fact that all of the energy supplied by the source is converted to another form by the resistor alone. We will find that conservation of energy has other important applications in circuits and is a powerful tool in circuit analysis.

The sizes of the symbols in the equation change to match the circuit diagram. Section Summary A simple circuit is one in which there is a single voltage source and a single resistance.

There is a voltage or drop across a resistor, caused by the current flowing through it, given by.

Conceptual Questions The drop across a resistor means that there is a change in potential or voltage across the resistor. Is there any change in current as it passes through a resistor?

## Ohm’s Law - How Voltage, Current, and Resistance Relate

How is the drop in a resistor similar to the pressure drop in a fluid flowing through a pipe? What current flows through the bulb of a 3. Calculate the effective resistance of a pocket calculator that has a 1.

How many volts are supplied to operate an indicator light on a DVD player that has a resistance of , given that What is the voltage drop in it when 5. What is the effect on the appliance? Thus, if the voltage drop across the extension cord is large, the voltage drop across the appliance is significantly decreased, so the power output by the appliance can be significantly decreased, reducing the ability of the appliance to work properly.

A power transmission line is hung from metal towers with glass insulators having a resistance of What current flows through the insulator if the voltage is kV?

## EMF & Internal Resistance - A-level Physics

Some high-voltage lines are DC. Skip to content Increase Font Size.

## Ohm’s Law - How Voltage, Current, and Resistance Relate

Explain what an ohmic material is. Describe a simple circuit. Resistance and Simple Circuits If voltage drives current, what impedes it? A simple electric circuit in which a closed path for current to flow is supplied by conductors usually metal wires connecting a load to the terminals of a battery, represented by the red parallel lines.

The zigzag symbol represents the single resistor and includes any resistance in the connections to the voltage source. Calculating Resistance: An Automobile Headlight.

## Resisitors in Series

The voltage drop across a resistor in a simple circuit equals the voltage output of the battery. Making Connections: Conservation of Energy. Previous: Current.

Next: Resistance and Resistivity.