Energy Flashcards
(45 cards)
What happens if we apply too great a force to a spring?
The extension will no longer be directly proportional to the force applied to the spring, as it has stretched beyond the limit of proportionality.
It will not return to its original length if we remove the forces.
What is the unit for spring constant?
N/m
What is gravitational potential energy?
The energy stored in an object due to its position above the earth’s surface.
What is the unit for gravitational field strength?
N/kg
What is meant by specific heat capacity?
The amount of energy needed to raise the temperature of 1kg of a substance by 1 degrees Celsius.
What is the unit for specific heat capacity?
J/kg *C
What is the Law of Conservation of Energy?
Energy can be transferred usefully, stored or dissipated but it cannot be created or destroyed.
What is the Law of Conservation of Energy?
Energy can be transferred usefully, stored or dissipated but it cannot be created or destroyed.
What is meant by a system?
An object or a group of objects.
In a closed system, no energy can enter or leave.
How do you reduce unwanted energy transfers?
Reducing friction:
- use a lubricant eg oil
- remove air particles
How do you reduce unwanted energy transfers?
Reducing friction:
- use a lubricant eg oil
- remove air particles
Bungee Jumper:
At the start, all of the energy in the system is gravitational potential energy.
As the jumper falls, energy is transferred from the gravitational potential energy store to the kinetic energy store.
When the rope tightens, the kinetic energy store is now at its maximum.
When the rope is fully extended, the kinetic energy is zero as they’re not moving.
All of the energy has been transferred to the elastic potential energy store.
The bungee rope recoils and energy is transferred back to the kinetic energy store.
During the ascent, energy transfers from the kinetic energy store back to the gravitational potential energy store.
The bungee jumper never returns to the original position because energy is dissipated as thermal energy:
Due to friction with air particles.
And stretching effects in the bungee rope which is not fully elastic.
What is work?
This is done whenever energy is transferred from one store to another.
Mechanical work: using a force to move an object.
Electrical object: involves a current transferring energy.
What is work?
This is done whenever energy is transferred from one store to another.
Mechanical work: using a force to move an object.
Electrical object: involves a current transferring energy.
What happens when a driver applies the brakes?
The brake presses against the wheel. This creates friction between the brake and the wheel.
The kinetic energy store of the car is transferred to the thermal energy store in the brakes. The temperature of the brakes increases and the car slows down and stops.
What is power?
The rate at which energy is transferred or the rate at which work is done.
How do you increase the efficiency of energy transfer?
Use pan with a wider base and a lid- reduce unwanted transfer of thermal energy.
Using a pan to heat water means a lot of thermal energy goes into heating the pan itself- so we can use a heating element inside the water like in a kettle.
Metal is a good conductor of heat so thermal energy will escape the pan into the air.
Plastic has a lower thermal conductivity.
How do you increase the efficiency of energy transfer?
Use pan with a wider base and a lid- reduce unwanted transfer of thermal energy.
Using a pan to heat water means a lot of thermal energy goes into heating the pan itself- so we can use a heating element inside the water like in a kettle.
Metal is a good conductor of heat so thermal energy will escape the pan into the air.
Plastic has a lower thermal conductivity.
Thermal conductivity:
The higher the thermal conductivity of a material, the higher the rate of energy transfer by conduction across that material.
How are modern houses built?
Two layers:
External brick wall and internal breezeblock wall.
Between the walls is a cavity. This gives these homes a high thermal conductivity. A lot of thermal energy transfers out of the house, so we spend a lot of money heating homes.
To correct this, builders pack the cavity with an insulating material with very low thermal conductivity.
How else can thermal energy escape in a house?
Windows:
Single glazed windows have a very high thermal conductivity.
Double glazed windows have low thermal conductivity.
Roof:
Use loft insulation. This has a low thermal conductivity, reducing the rate thermal energy passes through
How do you reduce thermal energy transfer from a house?
Use materials with a low thermal conductivity.
Thick walls.
Required Practical: Specific Heat Capacity
Place a beaker on a balance and press zero.
Now add oil to the beaker and record the mass of the oil.
Place a thermometer and an immersion heater into the oil.
Read the starting temperature of the oil.
Wrap the beaker in insulating foam to reduce thermal energy transfer to the surroundings.
Connect a joulemeter to the immersion heater.
Time for thirty minutes to allow the temperature to rise enough.
Read the total number of joules of energy that passed into the immersion heater.
Read the final temperature of the oil.
Calculate specific heat capacity.
What are the sources of inaccuracy in the SHC practical?
Thermal energy passing out of the beaker into the air: use an insulator with a lower thermal conductivity.
Not all thermal energy passing into the oil: Ensure that the immersion heater is fully submerged.
Incorrect reading of thermometer: electronic temperature probe
Thermal energy not being spread through the oil: Stir.
