Enegry Flashcards
How to calculate gpe
Mass(kg) times hight(1m) times gravity
How do you calculate ke
Mass(kg) times 1/2 times velocity(m/s) square
How do you calculate epe (Electric potential energy)
Times the N/m and the M square the M and then divide by 2
How do you calculate mechanical work
Cm divide by 100 the answer you get times by your N
The law of conservation energy
Energy can be transferred usefully stored or displaced but it can not be created or destroyed
The law of conservation energy diagram
System object or a group of objects
A closed system is where no energy can enter or leave
Start have the max store of gpe
Swing has kinetic swings back up gpe
Friction at the fricted point and the part were air passed
It gradually gets hotter THESS PARTS OF THERMAL ENGRY are less useful scientists called it dissipated
Reducing unwanted energy transfers
We can reduce unwanted energy transfers by reducing friction
Use lubricants e.g oil on the fitted point
Remove air particles from around the pendulum
Energy transfers bungee jumper
All gpe as the person fall the gpe is transfer to kinetic energy when the rope starts to tithe the kinetic energy is at the maximum then when the rope is fully extended the kinetic energy is at 0 bc the person is not moving all energy at elastic reverses when it recoils
Bungee jumper
The bungee never return to its final position bc the energy is dissipated to thermal energy
Work is done
Work os done whenever engery is transferred to one store to another
See it in mechanical work using a force to move an object electrical invokes using a current to Transfer energy
Mechanical work
A dog pulling a sledge
Chemical energy stored in the dog to
Kinetic energy stored in the sledge acting in the sledge and the ground
Thermal energy stored in the sledge and the ground
Work done equation
Work done (j) = force (n) x distance (m)
Thermal conductivity
The higher the thermal conductivity of materials the higher the rate of energy transfer by conduction across that material
Reduce cooling buildings
Pack cavity with an insulating material which low the rate of thermal conductivity
Single glazed window
High thermal conductivity
Dubbed glazed low thermal conductivity
Thermal in roof of the house
Reduce by loft insulation
Power
Power is the rate which energy is transferred or the rate at which work is done
Power (w) energy transferred(j) divided by the time (s)
Power (w) work done (j) divide by the time (s)
Current
An electrical current is a flow of electrical charge around the circuit
This means to a negative end of the cell to the positive end we draw the current in the opposite direction
Current in parallel circuits
The current in the branches adds up the total current leaving the cell
Pd
The cell has a store of chemical energy this is transferred to the electrical energy which is carried electrons passing out the cell when the electrons pass through the components e.g the lamp electrical energy is transferred to other forms of energy
Pd voltage
A pd of 1 volt tells us that 1 joule of energy is transferred to each coulomb of charge that is moving through the circuit
The total pd across both lamps is the same s the pd across the cell
Pd parallel circuits
For component connected in parallel the pd across each component is the Same ALL WAYS ADD UP TO THE SAME AS THE TOP
Pd in battery’s
Thick lines 3 pd 9 3x9= 27 volts
Resistor in series in parallel
Resisters in series add together
Question 100 resisters 50 resisters 20volts
The resistance in series add together the current has to pass through each resister in turn it cannot bypass any resistor we could replace the one resistor with 2 resistor 150 resistor this is called equivalent resistors
We can. Not calculated the current I volts divided by resistance 20d divided by 150 = 0.13 to 2dp
Key fact resistance in parallel
The total resistance of two resistors in parallel is less than the resistance of the smallest individual resistors bc with two resistors in parallel we have two pathways for the current to take more total current will flow through the circuit if the current has increased but the potential difference has not changed then the total resistance must have decreased
LDR resistor
I’m dark condition the ldr has a high resistance however in the light the resistance of the Ldr is very low how or mobile phones screen turn off while we’re having conversations in the light (when the phone is not held to your ear ) the resistance 9f LDR is very low it takes very little energy for the current to pass through the LDR BC the pd across the LDR is very low bc the pd is shared between components in series the pd across the lamp is large so the lamp lights up the screen if the phone is held to a persons ear the LDR in darkness the resistor of LDR rises sharply now it takes a great deal of energy for the current to pass through the LDR so the pd across the LDR is very high this mean that less electrical energy is available for the lamp the pd across the lamp is not very low the lamp becomes very dim
LDR resistor
I’m dark condition the ldr has a high resistance however in the light the resistance of the Ldr is very low how or mobile phones screen turn off while we’re having conversations in the light (when the phone is not held to your ear ) the resistance 9f LDR is very low it takes very little energy for the current to pass through the LDR BC the pd across the LDR is very low bc the pd is shared between components in series the pd across the lamp is large so the lamp lights up the screen if the phone is held to a persons ear the LDR in darkness the resistor of LDR rises sharply now it takes a great deal of energy for the current to pass through the LDR so the pd across the LDR is very high this mean that less electrical energy is available for the lamp the pd across the lamp is not very low the lamp becomes very dim
Thermistor
The resistance of a thermistor decreases if the temperature increases low temperature high resistance thermistor high temperature thermistor fall to a low level under cool condition the resistance of a thermistor is high mean it take a lot of energy for the current to pass through the thermistor bc the pd across the thermistor is high the pd is shared between components in series so pd across the fan is small the fan operates at a very low speed if the computer gets hot the resistance of the thermistor falls now it takes much less energy for current to pass through the thermistor means that the pd across the thermistor is now very low so more electrical energy is available for the fan this mean the pd across the fan very high so the fan powers up to high speed cooling the computer back down
Practical 3 resistance
Tape meter rule wire
Crocodiles clips
Straight line passes tho zero the resistance of the wire is directly proportional to the length
Practical 3 resistance
Tape meter rule wire
Crocodiles clips
Straight line passes tho zero the resistance of the wire is directly proportional to the length
Practice 4
Battery wire resistor ammeter and variable resistor
Voltmeter in parallel
Use the voltmeter to read the pd across resistor ammeter to read the current through the resistor records on a table
New we adjust variable resistor and record the new reading on the voltmeter and ammeter do 7 time now we switch the directions on the battery so it’s facing backwards pd have reversed the voltmeter and ammeter should now be in negatives numbers take 7 times
At the end have a graph going past 0
The resister is a ohmic conductor when we switch the direction we still get a straight line pass through 0
Some thing but no resistance with a lamp
We get a curvy graph some thing with a diode extra resistor bc diode is very easily damaged by a high current need a miller ammeter repeat 7 times backwards and forward battery only for a diode we only get a current when it’s at 0,6 or 0,7 volts nothing when reversed bc when reversed diode has a high resistance
Energy transfers application
Blender and fan
Electrical energy kinetic energy on the motors
Iron and kettle electrical energy
Thermal energy both designed to get. Hot
Hair dryer washing machine
Electrical energy transfer to kinetic energy of the motor and thermal energy
Motor moves air through the hair dryer heats the air washing machine heating electric heats the water meter turns the drum to heat the clothes
All have a power rating at which energy is transferred 1 watts (w) is 1 j per second
