Topic 7) Work, Power & Efficiency Flashcards
what is a thermistor?
a component where resistance changes with its temperature
where is the thermistor used?
in temperature sensors e.g fire alarms
direct current
electricity made in batteries, one direction current
alternating current
electricity from the mains current moves back and forth
electricity resistance
a measure of how much material tries to stop electric current passing through it
LDR
light dependent resistor
what LDRs respond to?
light changes
where can LDRs be used?
in street lamps
LED
light emitting diode
what is power?
the rate of energy transfer per second
what are the units of power?
watts
what happens when work is done to an object?
energy is transferred
what is the rate at which energy is transferred?
power
what is the equation for power?
power = work done / time taken
how is energy transferred?
by different energy transfer pathways
what are the energy transfer pathways?
mechanical
electrical
heating
radiation
what is the mechanical working pathway?
when a forces acts on an object (e.g. pulling, pushing, stretching, squashing)
what is the electrical working pathway?
a charge moving through a potential difference (e.g. current)
what is the heating (by particles) pathway?
energy is transferred from a hotter object to a colder one (e.g. conduction)
what is a (heating by) radiation?
energy transferred by electromagnetic waves (e.g. visible light)
what do sankey diagrams represent?
energy transfers
what does the principle of conservation of energy state?
energy cannot be created or destroyed, it can only be transferred from one store to another
when is energy transferred?
when things happen
what does work done depend on?
the force and how far the force moved
what is the equation for energy?
energy = force x distance
what is work done?
the transfer of energy
what makes one machine more powerful than another?
the volume of watts released / created
what is power measured in?
watts
what is the equation of?
power = energy / time
what are the variables that effect gravitational potential energy?
height, mass, gravitation field strength
what is gravitational potential energy?
the ability to make it move
what is the equation for for gravitational potential energy?
mass x gravity x height
what is the equation for potential energy?
1/2 x mass x velocity^2
what is the equation for efficiency?
(useful energy out) / (total energy in)
ways to improve efficiency?
design to create more aerodynamic
insulate heat
reduce friction
