Electric Potential Current February 2 2018 Potential difference

Electric Potential & Current February 2, 2018

Potential difference (V) Recall Work: W = F d cos(q) In order to bring two like charges together work must be done. In order to separate two opposite charges, work must be done. The greater the charge the monkey pushes, the more work he has to do. The closer he brings the charge to the other charge, the harder for him it is. Poor monkey

Potential difference (V) Recall Work: W = F d cos(q) In order to bring two like charges together work must be done. In order to separate two opposite charges, work must be done. Electrical potential difference (V or ΔV) is the amount of work required, per unit charge, to move a charge from point A to point B. The SI unit of electric potential is the volt.

Potential difference (V) Point A: Low potential spot Point B: High potential spot Charges will naturally move from high potential to low potential (the electric force does the work!). The monkey has to do work / input energy to move charge from low potential to high potential.

Potential Difference (V) & Circuits What is the role of a battery in a circuit? Batteries supply energy to maintain a potential difference across the circuit.

Potential Difference (ΔV) & Circuits What is the role of a battery in a circuit? Batteries supply energy to maintain a potential difference across the circuit. 1) A 12 V battery means that the + terminal has an electric potential that is 12 V higher than the – terminal.

Potential Difference (ΔV) & Circuits What is the role of a battery in a circuit? Batteries supply energy to maintain a potential difference across the circuit. 1) A 12 V battery means that the + terminal has an electric potential that is 12 V higher than the – terminal. 2) Charges flow through the external circuit (the wire) from high to low potential.

Potential Difference (ΔV) & Circuits What is the role of a battery in a circuit? Batteries supply energy to maintain a potential difference across the circuit. 1) A 12 V battery means that the + terminal has an electric potential that is 12 V higher than the – terminal. 2) Charges flow through the external circuit (the wire) from high to low potential. 3) As the charges flow through the circuit, they ‘lose’ energy to circuit elements such as lights and motors

Potential Difference (ΔV) & Circuits What is the role of a battery in a circuit? Batteries supply energy to maintain a potential difference across the circuit. 1) A 12 V battery means that the + terminal has an electric potential that is 12 V higher than the – terminal. 2) Charges flow through the external circuit (the wire) from high to low potential. 3) As the charges flow through the circuit, they ‘lose’ energy to circuit elements such as lights and motors 4) By the time the charges get to the end terminal, they have used up 12 V of potential

Potential Difference (ΔV) & Circuits What is the role of a battery in a circuit? Batteries supply energy to maintain a potential difference across the circuit. 1) A 12 V battery means that the + terminal has an electric potential that is 12 V higher than the – terminal. 2) Charges flow through the external circuit (the wire) from high to low potential. 3) As the charges flow through the circuit, they ‘lose’ energy to circuit elements such as lights and motors 4) By the time the charges get to the end terminal, they have used up 12 V of potential 5) The battery supplies the energy necessary to ‘push’ the charges back to high potential

Potential Difference (ΔV) & Circuits As charges ‘lose’ energy to different circuit elements, the electric potential decreases. This is known as voltage drop. All of the electric potential difference– i. e. all of the voltage -- is used up by the end of the circuit. Nearly all of the potential is lost across circuit elements; we will ignore the very small amount lost through the wires.

Terminology Fun 1. The variable we use for potential difference and the unit for potential difference (volts) are both V. 2. Don't let that confuse you when you see V = 1. 5 V 3. Electrical potential difference can also be described by the terms, electrical potential, voltage drop, potential rise, electromotive force, and EMF. These terms may differ slightly in meaning depending on the situation.

Check your understanding Compare an electric circuit to a roller coaster ride. What is the difference in height from the top to the bottom of a rollercoaster analogous to in a circuit? What is the motor that pulls the rollercoaster up the hill analogous to in circuit?

Check your understanding Compare an electric circuit to a roller coaster ride. What is the difference in height from the top to the bottom of a rollercoaster analogous to in a circuit? potential difference What is the motor that pulls the rollercoaster up the hill analogous to in circuit? battery

Check your understanding If a battery provides a high voltage, it can ____. 1. 2. 3. 4. do a lot of work over the course of its lifetime do a lot of work on each charge it encounters push a lot of charge through a circuit last a long time

Check your understanding Compared to point D, point A has … 1. 12 V higher potential energy 2. 12 V lower potential energy 3. Exactly the same potential energy The electrical potential energy is 0 at … 1. A 2. B 3. C 4. D

Check your understanding Compared to point D, point A has … 1. 12 V higher potential energy 2. 12 V lower potential energy 3. Exactly the same potential energy The electrical potential is 0 at … 1. A 2. B 3. C 4. D

Check your understanding Energy is required to move a charge from… 1. Point A to point B 2. Point B to point C 3. Point C to point D 4. Point D to point A The energy required to move +2 C of charge from D to A is 1. 0. 167 J 2. 2 J 3. 6 J 4. 24 J

Check your understanding Energy is required to move a charge from… 1. Point A to point B 2. Point B to point C 3. Point C to point D 4. Point D to point A

Electric Current

Closed vs. Open Circuits No, the switch is open, so the path is not complete Yes, charge will flow, BUT the light will not light No, the circuit needs to go from + to - Maybe! If one battery has higher V than the other

Direction of Current is defined as the direction positive charges would flow • From high potential to low potential • From + side of battery to – side of battery Fun Fact Benjamin Franklin defined current in this manner long before we knew much about charges. Now, we know that positive charges stay put and negative charges flow. So, electrons actually flow opposite current.

Calculating Current An important note about current: Although potential decreases across a circuit, current is the same everywhere in a circuit!

Circuit Analogy – CFU

Circuit Analogy - CFU E F B C A