The sun and other stars Flashcards
What does studying the radiation emitted by stars, such as the Sun, helps us to understand?
Studying the radiation emitted by stars, such as the Sun, helps us to understand the processes that occur when stars are formed, create new elements and eventually die. There are several types of star, depending on their age and mass. And there is some convincing evidence of ‘extrasolar’ planets that orbit hundreds of nearby stars, other than the Sun.
How do Electrons move between energy levels?
Electrons orbit in fixed energy levels around the nucleus inside an atom. They can move between these energy levels when they absorb energy (by moving to higher energy levels) or when they release energy (by moving to lower energy levels
are several energy level transitions possible within one type of atom ?
There are several energy level transitions that are possible within one type of atom - so an element absorbs and emits energy at a range of characteristic frequencies.
an element absorbs and emits energy at a range of…………… …………………
an element absorbs and emits energy at a range of characteristic frequencies.
It is common to measure temperature on what scale?
It is common to measure temperature on the Celsius scale, with ice melting at 0oC and water boiling at 100oC.
Physicists often prefer to use a different scale - what is 0 K is defined as? .
Physicists often prefer to use the Kelvin scale - on which 0 K is defined as absolute zero.
What is absolute zero?
This is the coldest temperature possible. At absolute zero, all the particles in a substance stop moving. They have no energy left to lose, so the substance cannot get any colder.
An increase in temperature of ten degrees Celsius is the same as an increase of what Kelvin? Converting is easy, as long as you remember that absolute zero (0 K) is -?
An increase in temperature of ten degrees Celsius is the same as an increase of ten Kelvin. This makes converting between them quite easy, as long as you remember that absolute zero (0 K) is -273oC.
How do you convert from Kelvin to degrees Celsius?
To convert from degrees Celsius to Kelvin, add 273.
To convert from Kelvin to degrees Celsius, subtract 273.
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How do you convert from degrees Celsius to Kelvin?
To convert from degrees Celsius to Kelvin, add 273
When a gas cools down what happens to the particles?
They lose energy.
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As mass is fixed, does the velocity of the particles decrease or increase as gas cools down?
decreases.
If a gas of fixed mass and volume is cooled down, what will happen to its pressure? Why is this?
If a gas of fixed mass and volume is cooled down, its pressure will decrease steadily. This is because each particle takes longer to reach the walls of the container, and therefore will do so less frequently and with less momentum.
If a gas of fixed mass and pressure is cooled down,what happens to its volume? why is this?
If a gas of fixed mass and pressure is cooled down, its volume decreases steadily. This is to compensate for the decreased frequency of collisions that are also weaker.
As the pressure or volume of a gas decreases, what happens to the temperature ?
As the pressure or volume of a gas decreases, the temperature will approach absolute zero (the coldest temperature possible).
At what point will the particles have lost all of their energy ? (so there will be no collisions with the walls of the container and therefore no pressure)
Absolute zero has a value of -273oC (0 K). This is the point at which the particles will have lost all of their energy, so there will be no collisions with the walls of the container and therefore no pressure
The pressure of a gas is caused by the particles ………… with the sides of the container, exerting a ………. per unit of area. The ………….. depends on the frequency of collisions and the force of the particles’ momentum
Pressure and volume
The pressure of a gas is caused by the particles colliding with the sides of the container, exerting a force per unit of area. The pressure depends on the frequency of collisions and the force of the particles’ momentum (the momentum is calculated by multiplying the mass of a particle by its velocity).
The momentum is calculated by ?
multiplying the mass of a particle by its velocity
The unit of pressure is what?
The unit of pressure is the pascal (Pa)
what is a pascal (Pa)?
pascal (Pa) - which is the same as the force of one newton spread over an area of 1 square metre.
If the volume of a container containing a gas is halved, what happens to the pressure? What must the temperature remain?
If the volume of a container containing a gas is halved, the pressure doubles. This relationship only works if the temperature remains constant
How can the gas law be summarised in an equations?
pressure x volume = constant
This relationship only works if the temperature remains constant
As the temperature increases, what happens to the particles ? What does this do to them?
As the temperature increases, the particles have more energy and move faster. This increases their momentum and makes them collide with the sides of the container with more force.
If the volume is kept constant, what is the effect of doubling the temperature?.
If the volume is kept constant, the effect of doubling the temperature will be to double the pressure.