Ch. 5.3 Energy in Electrical Systems

Moving Charges and Magnetic Fields Moving charges, like those in an electric current, produce magnetic fields.Moving charges, like those in an electric current, produce magnetic fields. The magnetic field around a wire forms a circular pattern around the wire.The magnetic field around a wire forms a circular pattern around the wire. The direction of the magnetic field depends on the direction the current flows.The direction of the magnetic field depends on the direction the current flows. The strength of the field depends on the amount of current flowing.The strength of the field depends on the amount of current flowing.

Electromagnets - 1 An electromagnet is a temporary magnet made by placing a piece of iron inside a current-carrying wire.An electromagnet is a temporary magnet made by placing a piece of iron inside a current-carrying wire. The strength can be increased by adding more turns of wire or increasing the amount of current.The strength can be increased by adding more turns of wire or increasing the amount of current. The north and south poles of the electromagnet can be reversed by reversing the direction of the current.The north and south poles of the electromagnet can be reversed by reversing the direction of the current.

Electromagnets - 2 Magnetic properties can be controlled by varying the amount of current.Magnetic properties can be controlled by varying the amount of current. A galvanometer is a device that uses an electromagnet to measure electric current.A galvanometer is a device that uses an electromagnet to measure electric current.

Electric Motors An electric motor is a device that changes electrical energy into mechanical energy.An electric motor is a device that changes electrical energy into mechanical energy. An electric motor contains an electromagnet that is free to rotate between two poles of a fixed permanent magnet.An electric motor contains an electromagnet that is free to rotate between two poles of a fixed permanent magnet. A - Power Source B – Electromagnet C – Permanent Magnet

Electromagnetic Induction Electromagnetic induction is the production of an electric current by moving a loop of wire through a magnetic field or moving a magnet through a loop of wire.Electromagnetic induction is the production of an electric current by moving a loop of wire through a magnetic field or moving a magnet through a loop of wire.

Electric Generators An electric generator does just the opposite of an electric motor. It changes mechanical energy into electrical energy.An electric generator does just the opposite of an electric motor. It changes mechanical energy into electrical energy. This is accomplished by using electromagnetic induction – turning a coil of wire in a strong magnetic field.This is accomplished by using electromagnetic induction – turning a coil of wire in a strong magnetic field.

Generating Electricity Electricity in the home comes from power plants with huge generators.Electricity in the home comes from power plants with huge generators. Coils of electromagnets in the generators are connected to a turbine, which is a large wheel that rotates when pushed by wind, water, or steam.Coils of electromagnets in the generators are connected to a turbine, which is a large wheel that rotates when pushed by wind, water, or steam.

Chapter 5.4 Energy in Thermal System

Heat Engines Heat engines are device that convert heat energy into mechanical energy. These include:Heat engines are device that convert heat energy into mechanical energy. These include: –Internal combustion engines are engines that burn fuel inside the engine in chambers or cylinders. An example is a car engine. –External combustion engines burn the fuel outside the engine and then transfer the heat to the engine. An example is a steam locomotive.

Four-Stroke Engines Automobiles are four-stroke internal combustion engines. The four strokes that power the automobile are listed below.Automobiles are four-stroke internal combustion engines. The four strokes that power the automobile are listed below. –Intake Stroke – Piston raises, takes in fuel –Compression Stroke – piston compresses fuel in the cylinder in the cylinder –Power Stroke – Spark plug ignites fuel, forcing the piston upward forcing the piston upward –Exhaust Stroke – Piston moves downward, forcing exhaust out of the engine forcing exhaust out of the engine

Heat Movers Heat movers are devices that remove thermal energy from one location and transfer it to another location at a different temperature.Heat movers are devices that remove thermal energy from one location and transfer it to another location at a different temperature. Examples of heat movers include refrigerators and heat pumps.Examples of heat movers include refrigerators and heat pumps.

Measuring Temperature We generally use two temperature scales, Celsius, which is commonly used for most laboratory work and the absolute temperature scale, which is also called the Kelvin scale.We generally use two temperature scales, Celsius, which is commonly used for most laboratory work and the absolute temperature scale, which is also called the Kelvin scale. The Celsius scale is based on the freezing point and boiling point of water. The 0° point is the freezing point and the 100° point is the boiling point.The Celsius scale is based on the freezing point and boiling point of water. The 0° point is the freezing point and the 100° point is the boiling point.

Measuring Temperature - 1 The zero point on the Kelvin scale is the point at which the thermal energy of the substance is zero. It is impossible to lower the temperature below this point and, therefore, the temperature is referred to as absolute zero.The zero point on the Kelvin scale is the point at which the thermal energy of the substance is zero. It is impossible to lower the temperature below this point and, therefore, the temperature is referred to as absolute zero. Each increment on this scale is called a Kelvin. The degree symbol is not used with the Kelvin scale.Each increment on this scale is called a Kelvin. The degree symbol is not used with the Kelvin scale.

Celsius to Kelvin Conversions The difference between the Kelvin and Celsius scales is 273 increments, so 0° C is 273 K and 100° C is 373 K.The difference between the Kelvin and Celsius scales is 273 increments, so 0° C is 273 K and 100° C is 373 K. To convert from Celsius to Kelvin, add 273.To convert from Celsius to Kelvin, add 273. From Kelvin to Celsius, subtract 273.From Kelvin to Celsius, subtract  C = ______ K 12  C = 285 K12  C = ______ K 12  C = 285 K 273 K = ______  C 273K – 273 = 0° C273 K = ______  C 273K – 273 = 0° C