Investigating Resistance in Ohmic and Non-Ohmic Devices
Aim:
To compare the effects of increasing voltage on resistance in a lightbulb and rheostat.
Independent Variable
Increasing the voltage (V)
Dependent variable
Measuring the resistance
Control variables
Ammeter, Voltmeter, Wires, Battery, surface, time between turning on and off
Introduction:
The purpose of this experiment was to investigate the resistance in Ohmic and Non-Ohmic Devices. Ohm's law defines the relationship between voltage, current, and resistance in a circuit. It states that the electrical current flowing through a circuit is proportional to the voltage and inversely proportional to the resistance.
Electricity is the flow of electrons. Electrons surround the nucleus of an atom; the negative charge of an electron is equal to the positive charge of a proton. An atom can gain and lose electrons, when electrons are lost from an atom, the movement of these electrons creates an electric current.
Electrical resistance is a measure of how difficult it is for electrons to flow through part of a circuit. Resistance is measured in ohms and symbolized by the Greek letter omega (Ω). All substances resist current flow to a degree and are typically divided into two categories: conductors and insulators. Conductors are materials such as metals that offer little resistance, letting the electrons flow easily. Insulators such as rubber are materials that have a high resistance and restrict the flow of electrons — the higher the resistance, the lower the current flow.
Many factors affect resistance in a circuit such as the thickness, length, temperature, and material of the wire. A wider wire has less resistance than a narrow wire because it allows more current to flow through the extra space.
A longer wire has more resistance than a shorter one. The current has to travel further through a longer wire, increasing the chance of it colliding with particles of matter. Cooler wires have less resistance than warmer wires; this is because particles have less kinetic energy making them move slower. Consequently, they are less likely to collide with moving electrons in the current.
Hypothesis:
Increasing the voltage increases the resistance in non-ohmic devices, the resistance stays constant in Ohmic devices.
Apparatus:
-Battery
-Ammeter
-Voltmeter
-Rheostat
-Lightbulb
-Wires (x5)
*insert photo of diagram from sheet*
Risk Assessment:
Hazards
Ways to Minimize risk
What to do
Electrocution
Keep battery away from water and taps. Avoid touching the circuit when the battery is on.
Report to teacher
Call 000
Burned
Do not touch the circuit while battery is on, or straight after turning battery off.
Report to teacher
Go to the office
Equipment falling on someone
Keep working area clear and equipment a safe distance away from ledges.
Report to teacher
Go to the office if serious
Tripping over equipment
Keep floor and working area clear.
Don’t run.
Report to teacher
Go to the office if serious
Broken equipm...
