Physics Flashcards
What is heat a measure of?
Energy
What is temperature a measure of?
Average kinetic energy of particles in a substance
What is the unit for heat?
Joules (J)
What is the difference between heat and temperature?
- Heat is a form of energy and it is not specific to an object. Instead it describes the transfers from and to an object.
- Temperature is a measure of the average kinetic energy of particles in a substance. It is specific to an object.
Heat is the transfer of energy as a result of a difference in the temperature of two objects.
Are the scales for temperature absolute scales?
No, because they go below zero.
When can heat flow between two objects?
When there is a difference in their temperature.
What factors affect the rate of conduction between two objects?
1) Material
2) State of object
3) Surface area
4) Temperature difference
What are 9 types of energy?
1) Electrical
2) Light
3) Sound
4) Kinetic
5) Nuclear
6) Thermal
7) Gravitational potential
8) Elastic potential
9) Chemical
What is nuclear energy?
Energy released from nuclear reactions.
How do heat exchangers work?
They pump a cold liquid near where heat loss occurs in a device and use this hot water for other purposes.
Remember to revise the different transmission distances and uses of radio waves.
Pg 210
What happens to the braking distance when you double the velocity?
- The distance goes up by 4 times, because:
- The velocity goes up by 2 times, so kinetic energy goes up by v2, which is 4 times.
- So the brakes, which work according to E = F x d need twice the distance to stop the car.
What do brakes do work against?
The kinetic energy of the car.
What does ABS brakes stand for?
Anti-locking Braking System
What do ABS brakes do and how do they work?
- They work to allow the driver to keep control of their car when braking hard
- They automatically pump the brakes on and off to prevent the brakes locking and the car skidding
What are regenerative braking systems?
- Put the motor in reverse to turn the wheels the opposite way in order to brake
- The motor acts as an electric generator, converting the kinetic energy of the car into chemical energy stored in the battery of the car
What is earthing?
Connecting an insulator to the ground so that any charge can flow to the earth and therefore there is no risk of sparks, etc.
How does a dust precipitator work?
- All emissions from a factory, etc. pass through the bottom of the precipitator, through a negatively charged grid.
- This gives them a negative charge.
- They are then attracted to positively charged earthed metal plates on the sides, where they stay until they eventually fall off and can be collected.
How does a defibrillator work?
- The defibrillator consists of two paddles connected to a power supply, which are placed on the patient’s chest.
- The paddles are insulated, so that the operator doesn’t receive a shock.
- Charge passes through the paddles into the patient, giving them a shock.
What happens to CELL voltages in series?
They add up.
What happens to CELL voltages in parallel.
They do not add up.
What happens to the current through CELLS in series?
It is the same through each cell.
What happens to the current through CELLS in parallel?
The currents through each cell sum together when the branches join.
Remember to revise electromagnetic induction.
Pg 255
What 4 factors affect the strength of the induced voltage in electromagnetic induction?
1) Strength of magnetic field
2) Cross-sectional area of coil
3) Number of turns on the coil
4) Speed of movement
What is the right-hand rule and what is it used for?
- Used to determine the direction of the current in electromagnetic induction
- The first 3 fingers on the right hand are held at right angles to each other
- Thumb = Force
- 1st finger = Magnetic field
- 2nd finger = Current
Describe the relationship between the voltage and current input and output from an ideal transformer.
I1V1 = I2V2
This is because power is conserved in an ideal transformer.
What is an isolating transformer?
- One that has the same number of turns in the primary and secondary coil, so the voltage is unchanged
- It can be found within the home in, for example, shaving razor socket
- It reduces the risk of being electrocuted
Give the formula for power loss in terms of current and resistance.
P = I2 x R
Describe how theories about the atom changed over time.
- First, John Dalton in 1804 built on the ideas of Democritus in saying that matter was made up of tiny inseparable spheres, but he also proposed that there were different kinds of atoms
- Then JJ Thomson managed to separate out electrons, disproving the previous theory. Instead he suggested that the electrons were located in a positive mass, which became known as the Plum Pudding model
- Then Rutherford and Marsden tried firing alpha particles at a thin gold sheet, expecting them to be all deflected by the sheet. Instead, most of the particles passed straight through and very few very reflected back. This led to the hypothesis that the positive charge was in a central nucleus, surrounded by electrons.
Who came up with the nuclear model of the atom?
Rutherford and Marsden
What is the unit for radiation dose?
Sieverts (Sv) or Millisieverts (mSv)
Give some examples of places where radiation dose may be increased.
- Certain underground rocks can cause higher levels of radiation at the surface, especially if they release radioactive radon gas (e.g. granite)
- Nuclear industry workers and uranium miners
- Radiographers
- High altitudes give less protection from the atmosphere
- Underground
What is the half-life of C-14 used in carbon dating?
5730 years
How can rocks be dated?
Looking at the relative composition of uranium and lead in the rock, since uranium decays to lead.
What is the half-life of uranium-238?
4.5 billion years
What is low-level radioactive waste and how is it disposed of?
- The majority of waste from hospitals and power plants, such as gloves and towels.
- It is buried in secure landfill sites.
What is intermediate-level radioactive waste?
- Some waste from hospitals and power plants, such as the metal cases of used fuel rods.
- It is sealed into concrete blocks, then put in steel canisters for storage.
What is high-level radioactive waste?
- Radioactive waste from power plants that generates a lot of heat.
- It is sealed in glass and steel, cooled for about 50 years and then moved into more permanent storage.
Intermediate and high-level radioactive waste could be buried deep underground. Why aren’t they usually?
It is difficult to find places that are geologically stable. Instead, the waste must be kept onsite at power plants.
Nuclear fuel is cheap. Why is nuclear power expensive?
The costs of the power plant, waste processing and eventual decommissioning is high.
What is cold fusion?
Nuclear fusion that occurs at room temperature. It is a theory that has not been reliably confirmed yet.
What is fluoroscopy?
- When a patient is placed between an x-ray source and a fluorescent screen. The intensity of x-rays reaching the screen depends on what they’ve passed through.
- The screen fluoresces when x-rays hit it, so a live image is created on the screen.
- The brightness is increased by an image amplifier, so a lower dose of x-rays can be used.
- A contrast medium is used to enhance soft tissue, which x-rays usually pass through.
- This can be used to diagnose problems in the way organs are functioning.
What are pulse oximeters used for?
The % oxygen in blood.
How does a pulse oximeter work?
- Oxygenated haemoglobin is red, while unoxygenated haemoglobin is more purple
- Two emitters of red light are placed on one side of a thin tissue (e.g. a finger) and a detector is placed on the other side
- The absorbance of the light can be used to determine how red the haemoglobin must be and therefore how oxygenated it is.
How is a reflection pulse oximeter different from a standard pulse oximeter?
A reflection pulse oximeter reflects red light off of RBC instead.
What does PET scanning stand for?
Positron Emission Tomography
How does PET scanning work?
- Positron-emitting isotope is injected into a patient
- The emitted positrons collide with electrons in the organs, leading to annihilation.
- This causes high-energy gamma rays to be emitted, which can be detected by 3 detectors around the body.
- Tumour cells will absorb more of the isotope, so they can be seen clearly in the image.
What is the resting potential of a muscle cell?
- The normal potential difference across the cell membrane, between the inside and outside
- It is usually about -70mV
How can the resting potential of a muscle cell be measured?
Using small needle electrodes.
Describe how muscle contractions work.
- The resting potential of muscle cells is usually about -70mV.
- An electric current can increase this to +40mV, which is called the action potential
- This passes along the cell, causing it to contract
What is the action potential of a muscle cell?
- The potential difference across the cell membrane when an electrical signal passes through that cell to contract it
- It is usually about 40mV
How are modern artificial pacemakers more advanced?
They can sometimes monitor the breath of the patient and adjust the heartbeat to suit their activity.
Remember to practice labelling an ECG.
Pg 286.
How can you work out the heart rate from an ECG?
1 / Time period
What is recorded on the y-axis of an ECG?
The action potential of the heart (V)
What is the peak frequency of a hot object?
The frequency of light that it emits most of.
What two things does the hotness of a star determine in terms of appearance?
- Peak frequency
* Luminosity
How does the hotness of a star determine the peak frequency?
The hotter the star, the higher the peak frequency (since there is more energy being emitted).
How does the hotness of a star determine the luminosity?
The hotter the star, the brighter it appears.
Compare the hotness of a red and blue star.
The blue star is hotter, since it has a higher peak frequency.
What is the photosphere?
The surface of a star that emits light.
