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Physics Paper 1 (P4 - Atomic Structure (Nuclear Radiation: (Unstable…
Physics Paper 1
P4 - Atomic Structure
An atom's radius is approx. 1 ÷ 100,000,000,000 (1 x 10^-11) metres, of which the nucleus takes up 1/10,000
An atom's nucleus is made up of positively charged protons and neutral neutrons. The nucleus is surrounded by electrons in specific orbitals
Electrons can move from their energy levels. They move up through the absorption of electromagnetic radiation, or down through the emission of EM radiation
The number of electrons in an atom is equal to the number of protons, which makes the overall charge equal 0
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Different Atomic Models:
Ancient Greek Model: atoms were thought to be the smallest parts matter could be divided into, they were depicted as cubes
Plum Pudding Model: the nucleus was a ball of positive charge, with balls of negative charge embedded into the surface
Nuclear Model: the alpha-scattering experiment showed the nucleus was a small ball in the middle of the atom of positive charge, with electrons on random orbits around the central point
Modern Nuclear Model: several other discoveries showed that the nucleus was made up of protons and neutrons with electrons on specified orbitals around the nucleus based on their energy levels
The alpha scattering experiment involved alpha particles being fired at a very thin sheet of gold leaf, which showed that most of the atom was empty space as most of the particles passed straight through, with electrons diverting them and the nucleus reflecting them drastically
Nuclear Radiation:
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Activity - the rate at which a source decays - is measured in becquerels (Bq). Count rate is the number of decays per second
The three types of radiation are as follows: alpha decay (the release of a helium nucleus, called an alpha particle here), beta decay (the release of an electron as a neutron turns into a proton), gamma ray (the release of a ray of electromagnetic radiation) and a neutron.
Radioactive decay is completely random, we can predict the number of counts per minute but cannot predict which atom will decay next
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P3 - Particle Model
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Energy is stored inside a system by the particles (atoms and molecules) that make up that system. This is called the system's internal energy, which is a combination of the kinetic and potential energy of all the particles in the system
Heating transfers energy to the particles in the system, increasing their kinetic energy. This increases the internal energy store of the system
The specific heat capacity of a substance is the energy required to raise the temperature of one kg of the substance by one degree centigrade
The specific latent heat of 'X' ('X' standing for fusion, evaporation or condensation) is the energy required for a substance to change state
The molecules in a gas air in a constant random motion. The kinetic energy of gas molecules is proportional to the temperature of the gas
Gases can be compressed or expanded by pressure changes. Pressure exerts a net force at 90 degrees to the surface of the container
Doing work on gases to compress them transfers energy to the internal store, which increases kinetic energy, which increases force exerted, which increases pressure
P1 - Energy
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Laws of Termodynamics
First Law: Energy cannot be created or destroyed, only transferred from one store to another
Second Law: the entropy of any isolated system always increases. Isolated systems spontaneously evolve towards thermal equilibrium - the state of maximum entropy of the system.
Third Law: the entropy of a system approaches a constant value as the temperature approaches absolute zero. The entropy of a system at absolute zero is typically zero.
Energy can be transferred usefully and any energy 'lost' is not destroyed, only involved in an unwanted transfer to the surroundings
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Main energy uses on Earth are transport, electricity generation and heating
P2 - Electricity
Static Electricity
Produced when certain insulating materials are rubbed together and electrons are transferred from one to another
The one that receives the electrons becomes negatively charged. The one that loses the electrons gains an equal positive charge
This electric charge creates an electric field around the objects. Opposite charges attract and similar charges repel. Any object placed in the field will experience a force
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Mains Electricity
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Mains connects to appliances using a three-core cable: brown is the live wire carrying 230V, blue is the neutral wire with a voltage of 0V and the safety wire is green and yellow striped; there to prevent an appliance from becoming active/shorting to the human
Step-up transformers are used to step up the voltage for transit around the country, reducing the current and thus the power lost. Step-down transformers then step the voltage back down to 230V for domestic use
Required Practicals
Energy
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Method
1) Take four test tubes and wrap in the different types of insulation, leaving one without any.
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Hazards and Risks
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Hot water so try to avoid spillages as this could lead to burns. Equipment may also get hot so try to not burn yourself.
Electricity
Title: Investigate the V-I characteristics of a filament bulb, a diode and a resistor at a constant temperature.
Method
1) Set up test circuit with three cells, an ammeter and a voltmeter over the component being tested.
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Hazards and Risks
The filament lamp will get hotter as the current increases and could cause burns. Allow the bulb to cool down before repeating the experiment or unscrewing it.
