Dynamic Electricity Flashcards
TWO TYPES OF ELECTRICITY
Static and dynamic
Static electricity
Static electricity is when you charge an object, and it repels or attracts other charged (or neutral) objects
Dynamic electricity
Current electricity the flow of electrons within a conducting material.
What can we measure in this Static situation?
Static electricity has a limited number of measurable variables:
1) number of electrons transferred ,
2) amount and sign of charge on the object (measured in C),
3) amount and type of electric Force between charged objects
(measured in N)
What could we measure in a
Dynamic Electricity system?
The movement of electrons (dynamic electricity) introduces new quantities to measure, for example:
the rate of electron flow (how much charge per second is travelling in the wire), the “pressure” pushing the electrons through the wire (voltage/potential difference),
the resistance to electron flow, etc.
Power source
Power source: Source of energy used to move electrons in a circuit, creates a potential difference compelling the electrons to move.
Example: Battery
Conducting wires
Conducting Wires: Allows electrons to travel from one part of a circuit to another part. Carries the charges pushed by the power supply to the circuit elements, then back to the power supply.
Current
An electric current is the orderly flow of negative charges carried by electrons
The conventional direction of a current is from the positive terminal of a power supply towards the negative terminal. (This is opposite of Electron Flow.)
(Think back to our electric field drawings from static electricity: FROM positive TO negative!)
Circuit elements
Circuit Element(s): these items resist the flow of electrons and consume energy/voltage available to the circuit when they perform their tasks.
Ex: light bulb – converts electrical energy to light and heat
Open VS Closed circuit. What does it depend on?
Circuit functions depend on the flow of electrons.
If something prevents electrons from flowing (switch, broken wire, etc) ALL electron movement stops.
Open circuit = OFF, Closed circuit = ON
*Electrons cannot flow if they do not have a path back to their source
Current intensity
The Current Intensity measures how much charge per second is moving through the circuit at a particular point.
It is similar to the intensity of traffic flow on a highway, or water flow in a pipe or hose. per second
Greater intensity =
Greater intensity = more electrons are flowing
Direct Current (DC
Electrons travel through the conductors from one end to the other, pushed by the potential difference (voltage) of the DC power source (ex: battery).
Most electronic devices function on DC current. The “box” on power adaptors converts the AC current from the wall outlet to DC current for the electronic device.
Alternating current (AC)
Alternating Current (AC) – Electrons “wiggle” back and forth. This “wiggling” is caused by the AC power source. The motion is communicated from electron to neighboring electron all along the wire.
Power generating stations produce AC current. AC current is optimal for sending electricity long distances (DC current has too much loss).
AC current can power motors, heating elements, and other simple mechanical devices.
How do we measure the intensity of a current?
An Ammeter is used to measure the intensity of electric current.
It has to be placed in series (in line) with the circuit branch being measured.
(traffic analogy: to measure the amount of cars moving through the highway, you would install a car detector across the highway lanes)
Series vs parallel circuits
Series Circuit = No Branching
- The circuit does NOT branch out
- The current can only follow ONE path
Parallel Circuit = at least one path branches into many paths
The circuit does branch out
- The current can follow different path
Potential difference
Potential Difference is like the pressure or push that moves the electrons.
We calculate the amount of “pressure” (electric potential, or voltage) by measuring the amount of energy a unit of charge loses or gains as it goes through circuit components, from one point to another.
How do we measure potential difference?
A Voltmeter is used to measure the potential difference between two points in a circuit.
We measure the change of energy per unit charge, usually through a single circuit element (resistor, lightbulb, etc). We must connect the Voltmeter before and after the element to measure the change.
This is called connected in parallel
Electrical Resistance in a circuit
Electrical resistance is the ability of a material/object to hinder the flow of an electric current.
The role of resistors is to limit the flow of electrons.
Most electronic components/elements hinder the motion of electrons through the circuit.
Electrical Resistance is the ability of a material to resist the flow of electric current.
Components that transform electric energy also cause resistance examples:
Lights - transform electric energy into light & thermal energy
Toaster - transform electrical energy into thermal energy
Ohm’s Law - relationship between V, R & I
For a given constant resistance, the potential difference is directly proportional to current intensity
Directly proportional: As potential difference (V) increases so does intensity (I)
Resistance AND WIRES
Conductive wires are considered to have zero resistance
(but this is not quite true! Only superconductors have exactly zero resistance; “normal” conductive wires have near-zero resistance)
Larger Ohm = ___________Resistance. Smaller Ohm = __________ resistance.
Larger Ohm values offer electrons more resistance. Smaller Ohm values do not offer electrons much resistance.
Factors affecting resistance
Length
Temp
Area
Type of material
How length affects resistance
Longer materials have greater resistance
Resistance and area
Larger areas, less resistance
Temperature and resistance
Higher temperatures, higher resistance
Resistance and material
Iron has more electrical resistance than copper.
Power
Power depends on time
Power is the amount of work (In Joules) an electrical device can perform in one second.
P = E/T
Power is measure in units of Watts
What is a watt
1 watt = 1 joule per second
Nodes
The point at which a circuit separates into two or more paths and the point at which two or more branches merge into one are called NODES.
Parallel Circuit
Logistics
A parallel circuit contains branching paths.
The current leaving the battery separates and takes different paths.
The current intensity in the different paths will depend on the resistance of each individual path. The current in each branch is not necessarily equal.
The branching paths must reconnect and allow a path for electrons to return to the battery. (otherwise you’d have an open circuit, no current would flow at all)
If a circuit element breaks and creates an open circuit, the current is still able to flow through the other branches. Only the branch with the open circuit will be affected.
