Gas pressure and Radioactivity Flashcards
What is the equation for specific latent heat of fusion
Lf (J/Kg) = Energy E (J) / Mass M (Kg)
What is latent heat?
The energy transferred when a substance changes its state.
What is specific latent heat of fusion?
The energy needed to change the state of 1kg of the substance from solid to liquid at its melting point( without changing temperature).
What is the specific latent heat of vaporisation?
The energy needed to change state of 1kg of the substance from liquid to vapour at it’s boiling point ( without changing temperature).
What is the equation for specific latent heat of vaporisation?
Lv (J/Kg) = Energy E (J) / Mass M (Kg)
How can we measure the specific latent heat of ice or water?
By using a low voltage heater to melt the ice (or boil the water) and a joulemeter measures this, then repeats it’s readings at 5 minute intervals.
What is the pressure of a gas?
The total force exerted on a unit area of the surface.
Why does increasing the temperature of a sealed gas container increase the pressure of that gas?
Increase in energy with heat increases. kinetic energy of molecules. Average speed of molecules increases with increase of kinetic energy. This means the molecules hit the surfaces more often and more forcefully.
How can we prove the random motion of gas molecules?
Via the unpredictable motion of smoke particles in a smoke cell, viewed under a microscope.
Why can we see the random motion of smoke particles?
Because the smoke particles are bigger than air particles, and the glass cell contains air molecules moving erratically, pushing the smoke molecules randomly. The movement of the smoke we can see.
What is the random motion of tiny particles in a fluid called?
Brownian motion.
What happens to the volume of air in a tube when pressed?
It decreases as the pressure increases. As long as the compression happens slowly, the temperature of the air in the tube doesn’t change. This is because the gas loses energy by heating to its surroundings at the same rate as energy transferred to it.
What would happen if gas in a tube was compressed quickly?
The work done on the gas would increase the internal energy store and it’s temperature. This is because the gas will be transferred energy at a greater rate than it can lose it by heat to the surroundings.
Why is it when the volume of a fixed mass of gas at a constant temperature is reduced, the gas pressure increases?
The space the molecules move in is smaller, so they don’t travel as far between each impact with the surface of the container. They hit the surface more often, impacts per second increases and the force per square metre of surface. This is demonstrated by Boyle’s law - that if pressure is constant, so is volume. Their relationship is inversely proportional.
What is the equation for Boyle’s Law?
Pressure, P (Pa) x Volume V ( M cubed) = constant . This equation can be used if the mass and temperature of a gas doesn’t change.
Describe the relationship between mass, number of molecules, temperature and speed of molecules.
For a fixed mass of gas, the number of gas molecules is constant. If the temperature is constant, the average speed of the molecules is constant.
What is a radioactive substance?
A substance that spontaneously contains unstable nuclei, that becomes stable by emitting radiation (radioactive decay). The three main types of radiation that a radioactive substance emits are alpha, beta and gamma.
What did the Rutherford’s first investigation find out about the types of radiation?
That alpha radiation was stopped by paper and made up of positively charged particles ( two protons and two neutrons together), and so can be used to assess what is inside an atom. Beta radiation ( a positron e+ or electron e-) is more penetrating than alpha. It is blocked by a lead sheet or aluminium sheet.
What is radioactive decay?
The process of an unstable nucleus becoming more stable over time by spontaneously emitting ionising radiation. We cannot influence the process of radioactive decay.
What does Rutherford’s alpha particle scattering experiment show?
By counting the scatter and locations of a beam of alpha particles, it was found: most alpha particles pass through metal foil, the amount deflected off the foil decreased as the angle of firing and deflection increased ( fewer bounce off the foil at 90 degrees vs 60 degrees for example) and few particles could be deflected after 90 degrees.
What can be deduced from the Rutherford alpha particle scattering experiment, after it was found that alpha particles have patterns of deflection?
That there is a positively charged nucleus in each atom that is smaller than the atom because alpha particles are small enough to pass through the foil or deflect. The atom contains an area in the middle with a bigger mass (the nucleus). This model was accepted because it explained radioactivity in terms of what happens to an unstable nucleus when it emits radiation and also predicts the existence of neutrons. It was better than the plum pudding model as that couldn’t explain the angles of deflection.
What does Bohr’s theory of the atom state?
That the electrons in an atom orbit the nucleus at specific distances and specific energy levels. And that electrons can move to another orbit via absorbing electromagnetic radiation.
How do we represent the changes in numbers of protons and neutrons from alpha or beta decay?
There are changes in the atomic and mass numbers. If there is just a change in neutrons, the element is known as an isotope.
Describe alpha emission
An an alpha particle is made of two protons and two neutrons. It has a relative mass of 4 and a relative charge of +2. When an unstable nucleus emits an alpha particle it’s atomic number goes down by 2, and it’s mass number goes down by 4.
Describe Beta emission
A beta particle is from a nucleus with too many neutrons. So a neutron will change to a proton and be emitted with a beta particle (which is usually an e- ((electron)) ) A beta particle has a mass of 0 and a charge of -1
(( or +1 if it is rarely a positron which is an e+, but don’t worry about this - just an interesting fact)).
Describe Gamma emission
Gamma radiation is electromagnetic radiation from the nucleus of an atom and does not have a charge nor mass. it is much more penetrative and is only blocked by lead or concrete.
What is irradiation?
When radiation knocks electrons out of atoms, the atoms then become charged (the atom undergoes ionisation, the means of how is irradiation). Ionisation in a living cell can damage or kill it.
What is radioactive contamination?
The unwanted presence of materials containing radioactive atoms or other materials. The hazard comes from the radioactive decay of the nuclei of the atoms.
How do workers using ionising radiation reduce their exposure to radiation?
Keeping far away from the source - eg using extension tools to touch the material. Limiting time to exposure. Shielding behind thick concrete barriers or lead plates.
What is the half life of a radioactive isotope?
The average time it takes for the number of nuclei of the isotope in a sample to halve.
The number of atoms of a radioactive isotope and the count rate both decrease by half every half life. The count rate after n half lives = the initial count rate / 2n
