Electrical resistance facts for kids
|Electricity · Magnetism|
The electrical resistance of an electrical conductor is a measure of the difficulty of passing an electric current through that conductor. It explains the relationship between voltage (amount of electrical pressure) and the current (flow of electricity). With more resistance in a circuit, less electricity will flow through the circuit.
Resistance, discovered by Georg Simon Ohm in 1827, is the ratio between voltage and current. Ohm's law said that the voltage between any two points in a conductor changes directly as the current between the two points, given the temperature remains the same. He described it with the equation:
which models the ratio, where:
- is the resistance of the object, measured in ohms (Ω)
- is the voltage across the object, measured in volts (V)
- is the current going through the object, measured in amperes (A)
The resistance of a wire increases as it becomes longer and decreases as it becomes wider. (A simple analogy is a road - the more lanes there are, the less traffic there is.) The resistance R of a wire with a constant width, therefore, can be calculated as:
where is the length of the conductor, measured in meters [m], is the cross-sectional area of the conductor measured in square meters [m²], and ρ (Greek: rho) is the electrical resistivity (also called specific electrical resistance) of the material, measured in ohm-meters (Ω m).
Example: Calculate the resistance of copper wire with a radius of 2mm and a length of 5 meters.
- The resistivity () of copper is Ω m.
- The cross sectional area () is square meters
- The length () is meters
Images for kids
A 6.5 MΩ resistor, as identified by its electronic color code (blue–green–black-yellow-red). An ohmmeter could be used to verify this value.
The voltage (red) and current (blue) versus time (horizontal axis) for a capacitor (top) and inductor (bottom). Since the amplitude of the current and voltage sinusoids are the same, the absolute value of impedance is 1 for both the capacitor and the inductor (in whatever units the graph is using). On the other hand, the phase difference between current and voltage is -90° for the capacitor; therefore, the complex phase of the impedance of the capacitor is -90°. Similarly, the phase difference between current and voltage is +90° for the inductor; therefore, the complex phase of the impedance of the inductor is +90°.
Electrical resistance Facts for Kids. Kiddle Encyclopedia.