Transcript Presentation

Ch. 5.3
Energy in Electrical
Systems
Moving Charges and 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 direction of the magnetic field
depends on the direction the current
flows.
• 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.
• 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.
Electromagnets - 2
• Magnetic properties can be controlled by
varying the amount of 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 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.
Electric Generators
• 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.
Generating Electricity
• 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.
Chapter 5.4
Energy in Thermal System
Heat Engines
• 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.
– Intake Stroke – Piston raises, takes in fuel
– Compression Stroke – piston compresses fuel
in the cylinder
– Power Stroke – Spark plug ignites fuel,
forcing the piston upward
– Exhaust Stroke – Piston moves downward,
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.
• 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.
• 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.
• 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.
• To convert from Celsius to Kelvin, add 273.
• From Kelvin to Celsius, subtract 273.
• 12 C = ______ K
12 C + 273 = 285 K
• 273 K = ______C
273K – 273 = 0° C