physics

physics

1. P4 - Atomic Structure

   • Atoms consist of a nucleus containing protons and neutrons, surrounded by electrons in shells. The numbers of subatomic particles in an atom can be calculated from its atomic number and mass number.
     • An atom has a central nucleus. This is surrounded by electrons arranged in shells.
       • The nucleus is tiny compared to the atom as a whole: the radius of an atom is about 0.1 nm (1 × 10-10 m) the radius of a nucleus (1 × 10-14 m) is less than of the radius of an atom For comparison, the radius of a typical bacterium is 1 × 10-6 m and the radius of a human hair is about 1 × 10-4 m.
         • Subatomic particles The nuclei of all atoms contain subatomic particles called protons. The nuclei of most atoms also contain neutrons.
           • • The masses of subatomic particles are very tiny. Instead of writing their actual masses in kilograms, we often use their relative masses. The relative mass of a proton is 1, and a particle with a relative mass smaller than 1 has less mass.
               • The mass of an electron is very small compared to a proton or a neutron. Since the nucleus contains protons and neutrons, most of the mass of an atom is concentrated in its nucleus. Protons and electrons have electrical charges that are equal and opposite.
                 • The number of protons in an atom of an element is its atomic number. Remember that: all atoms of a given element have the same number of protons atoms of different elements have different numbers of protons An atom contains equal numbers of protons and electrons. Since protons and electrons have equal and opposite charges, this means that atoms are have no overall electrical charge. For example, the atomic number of sodium is 11. Every sodium atom has 11 protons and 11 electrons. It has 11 positive charges and 11 negative charges.

2. P2 - Electricity

   • The following symbols show the different components that can be found in an electrical circuit.
     • • Components Some of the more common components are: Switch A switch used to turn a circuit on (closed) and off (open). Lamp An electrical current heats the filament in a bulb so that it gives out light. Fixed resistor A resistor restricts or limits the flow of electrical current. A fixed resistor has a resistance that does not change.
         • Variable resistor Moving the position of the slider on this resistor, changes the resistance. A variable resistor is used in some dimmer switches and volume controls. Thermistor The resistance of a thermistor depends on its temperature. At low temperatures, the thermistor has a high resistance. As the temperature increases, the resistance decreases. A thermistor can be used in thermostats or heat activated fire alarms.
           • Light-dependent resistor (LDR) The resistance of a LDR depends on light intensity. At low light levels, the LDR has a high resistance. As the light intensity increases, the resistance decreases. A LDR can be used as a sensor in cameras or automatic lights that come on when it gets dark.
             • Semiconductor diode A semiconductor diode allows current to flow in one direction only. Current will not flow in the other direction. Diodes are used to convert an alternating current into a direct current.
               • Electrical charge and current There are two types of current: direct and alternating. In a direct current, the flow of electrons is consistently in one direction around the circuit. In an alternating current, the direction of electron flow continually reverses. Charge Electrons are negatively charged particles and they transfer energy through wires as electricity. Charge is a property of a body which experiences a force in an electric field. Charge is measured in coulombs (C). Since electrons are so small and one electron will not have much of an effect anywhere, it is more useful to refer to packages of electrons. One coulomb of charge is a package equivalent to 6,250,000,000,000,000,000 electrons.

Bilder und Dateien der Mindmap