Electrical Energy & Power

Big ideas Energy Power Potential energy Voltage Charge Current Resistance Calculating power from a turbine

What is energy? When scientists talk about ENERGY, they are referring to the ability to do work. When scientists talk about WORK, they are referring to a force over applied over a distance. ENERGY: ability to change the motion of an object

Quantifying energy The unit of measure for energy is joules, J. Energy is calculated by multiplying force times distance A joule is the same as newtons x meters Abbreviated: J = Nm It takes about one joule to lift one apple one meter high on Earth.

What is power? When scientists talk about POWER, they are referring to the rate at which energy is converted from one form to another.

Quantifying power The unit of measure for power is watts, W. Power is calculated by dividing energy by time A watt is the same as a joule per second A 60-W lightbulb converts 60 J of electric energy to light and thermal energy every second.

What is potential energy? When scientists talk about POTENTIAL ENERGY, they are referring to an object’s potential to do work. That is, the object is not doing work yet, but could. It is stored energy POTENTIAL ENERGY: stored energy

Look for potential energy… Gravitational field Raising an object above the ground Chemical bonds In fuels In food Elastic Compressed spring Stretched rubber band Electrical field Moving “like charges” closer together

Big ideas Energy Power Potential energy Voltage Charge Current Resistance Calculating power from a turbine

Opposites attract… You have probably heard that “opposites attract and likes repel”. When scientists refer to “opposites” and “likes”, they are referring to ELECTRIC CHARGE.

Quantifying charge The unit of measure for charge is coulombs, C. The charge on one electron is 1.6 x C A coulomb a LOT of charge When you rub a balloon on your head, you transfer ~1/1,000,000 C

Electrical potential energy If you can force like charges together, they behave like compressed microscopic springs. The closer you push the charges together, the harder they push against each other. Electrical energy can be stored this way.

Quantifying electrical potential energy The unit of measure for electrical potential energy or, more commonly, voltage is volts, V. Voltage is calculated by dividing potential energy of concentrated charges by the amount of charge A volt is the same as a joule per coulomb A 9-V battery can provide 9 joules of energy to every coulomb of charge in the circuit.

What is current? When scientists talk about current, they are referring to the rate at which something flows by. When they talk about ELECTRIC CURRENT, they mean the rate at which charge flows by. Current: rate at which charge passes through a circuit

Quantifying current The unit of measure for current is amps, A. Current is the rate at which charge flows by a particular point. An amp is the same as a coulomb per second The wires in your house can safely carry up to 15 amps

Difference between potential and current Consider flow of water About the same gravitational potential A romantic spot for a swim with your special someone A disastrous spot for a swim with anyone

Danger? The difference is the current! A car battery maintains a potential difference of just 12 J/C and will seriously harm or kill you if you complete the circuit with your body. Check this from UC Denver Med SchoolUC Denver Med School A Van der Graaf generator can build up a voltage of 20,000 J/C. It’s shocking to touch but not typically dangerous.

Relationship between voltage and current If you have a higher voltage, it means that you have more energy per charge. If you have higher energy per charge, charges will be pushed faster, i.e., current will be higher. voltagecurrent voltagecurrent  voltagecurrent= ??

Relationship between voltage and current Examples: Motors Speakers Lights Heating elements Fans voltagecurrent= ?? The rate at which charge flows through a circuit will depend on how hard it is to get through the circuit. We call that ‘hardness’ RESISTANCE voltagecurrent= resistance x

What is resistance? When scientists refer to RESISTANCE, they are referring to how hard it is for current to pass through an element in a circuit. Resistance: ratio of how hard charge is pushed (voltage) to how much gets through (current)

Quantifying resistance The unit of measure for resistance is ohms, . An ohm is the same as a volt per amp Dry skin has a resistance of 100,000 . Wet skin has a resistance of 1,000 

Big ideas Energy Power Potential energy Voltage Charge Current Resistance Calculating power from a turbine

Calculate power from pieces on a circuit We measured voltage and we know resistance. How do we calculate power?

Example Calculate the power of a turbine that produces an average voltage of 4 V in a circuit that has a 2  resistor. Given: Unknown: Equation: Substitute: Solve:

Calculate energy from turbine We calculated power. How much energy did the turbine produce?

Example Calculate the amount of electrical energy produced by a turbine with an average power of 6 W over 60 seconds. Given: Unknown: Equation: Substitute: Solve: