# GCSE Physics P5 (OCR)

Flashcards by Usman Rauf, updated more than 1 year ago More Less Created by Josh Price almost 6 years ago Copied by Usman Rauf almost 6 years ago
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### Description

GCSE Physics Flashcards on GCSE Physics P5 (OCR), created by Usman Rauf on 04/16/2015.

## Resource summary

 Question Answer What happens when two objects are rubbed together? They become charged because electrons are transferred from one object to another. Objects with similar charges ______. Objects with opposite charges ________. Repel Attract Why does a charged rod pick up pieces of paper? If a negatively charged rod comes near, it repels negative charges in the paper to the far end. This leaves a surplus of positive charges at the near end. The attraction between these charges and the negatively charged rod is stronger than the repulsion between the negative charges in the paper and the rod. Are electrons negatively or positively charged? Negatively What is electric current? A flow of charge What is electric current measured in? Amperes What is an electric current in metallic conductors? A movement of free electrons that are present throughout such materials. In metal conductors there are ______ charges free to move. In an insulator there are ____ charges free to move. Many Few The ______ the voltage of the battery in a circuit, the ______ the current. Larger Bigger Components _______ the flow of charge between them. Resist. (Eg. Resistors, lamps, motors) The _______ the resistance in a circuit, the _______ the current will be. Larger Smaller Why can the resistance of connecting wires usually be ignored? Because it is so small. What happens when electric charge flows through a component? Work is done by the power supply, and energy is transferred from it to the component and its surroundings. What is power? A measure of the rate at which an electrical power supply transfers energy to an appliance of device and its surroundings. What is power measured in? Watts (W) Power = _________ x _________ Voltage x Current What happens to resistors when an electric current runs through them? They get hotter. This is caused by collisions between the moving charges and stationary ions in the wire. What effect does this heating have on a lamp filament? It makes it hot enough to glow. How does the resistant of and LDR vary with light intensity? As light intensity increases, resistance decreases. How does the resistance of a thermistor vary with temperature? Resistance decreases as temperature increases. What happens to the resistance if there are two (or more) resistors in series? The resistance increases because the battery has to move charges through both of them. What happens to the resistance if there are two (or more) resistors in parallel? The resistance is decreased because there are more paths for charges to move along. What is resistance measured in? Ohms Resistance = _______ / _________ Voltage / Current How does the current through a component vary with voltage across it when the resistance stays the same? The higher the voltage, the higher the current. If current increases by one, then voltage increases by two. How should a voltmeter be connected to measure the potential difference between any two chosen points? It should be connected at both of the chosen points. What is the voltage across a battery the measure of? The 'push' of the battery on the charges in the circuit. What is potential difference? Another term for voltage. The work done when a coulomb of charge passes between two points. How does the potential difference relate to the work done by a charge? The bigger the charge, the bigger the potential difference. (Because water is being pumped higher, so it has further to fall.) How does adding batteries in series effect the potential difference? The potential difference would increase. How does adding batteries in parallel effect the potential difference? It does not change. What happens to the current when two (or more) components are added in series to a battery? It stays the same through each component. What happens to the potential difference when two (or more) components are added in series to a battery? The potential differences across each component adds up to the potential difference across the battery because the work done on each unit of charge by the battery must equal the work done by it on the circuit components. What happens to the potential difference across a component when two (or more) components are added in series to a battery? The potential difference is largest across the component with the greatest resistance because more work is done by the charge moving through a large resistance than through a small one. What happens to the potential difference if the resistance of one component is changed when two (or more) components are added in series to a battery? It will results in a change in the potential difference across all of the components. What happens to the potential difference when two (or more) components are added in parallel to a battery? The potential difference across each component is equal to the potential difference of the battery. What happens to the current when two (or more) components are added in series to a battery? It is the same. What is mains electricity produce by? Generators How do generators produce a voltage? By electromagnetic induction What happens when a magnet is moving into a coil of wire? A voltage is induced across the ends of the coil, which causes an electric current in the circuit. What happens if the magnet is moving out of the coil? There is a voltage induced in the opposite direction. What happens if the ends of the coil are connected? A current will flow around the circuit. Describe how transformers are constructed. Two coils of wire are wound on an iron core. What will a changing current in one coil of a transformer cause? A changing magnetic field in the iron core, which in turn will induce a changing potential difference across the other transformer coil. What can a transformer do? Alternate the size of an alternating voltage. Vs/Vp = Ns/Np Voltage across secondary coil / Voltage across primary coil =Number of turns on secondary coil/ Number of turns on primary coil How is a magnet or electromagnet rotated within a coil of wire to produce a voltage across the ends of the coil? While the magnet moves into the coil, the magnetic field around the magnet changes. Magnetic field lines are 'cutting' the coil. This causes a potential difference (a voltage) across the coil. How can the size of this voltage be increased? - Moving the magnet in and out more quickly - Using a stronger magnet - Increasing the number of turns on the coil - Placing an iron core inside the coil How does the induced voltage across the coil of an a.c. generator change during each revolution of the magnet? The voltage and current change direction every half turn of the magnet. What is direct current? What is alternating current? D.C = The current is always in the same direction (eg. a battery). A.C. = The current changes direction. Is mains electricity an a.c supply or a d.c supply? A.C Why is A.C used for mains electricity? Because it is easier to generate than d.c. and it is easier and simpler to distribute over long distances. What voltage is mains domestic supply in the UK? 230 volts. How can the size of the alternating voltage produced by a generator be increased? - Using a stronger rotating magnet - Rotating the magnet faster - Using a fixed coil with more turns - Putting an iron core inside the fixed coil A _______-______ ____ can exert a force on a permanent ______, or another _______-______ ______ nearby. Current-Carrying Wire Magnet Current-Carrying Wire To make a motor, where is the current-carrying wire placed? In a magnetic field whose lines of force are at right angles to the wire. When placed here, what does the wire experience? A force at right angles to both the current direction and the lines of force in the field. What happens if the current-carrying wire is parallel to the lines of force of a magnetic field? It experiences no force. How can the motor effect result in a turning force on a rectangular current-carrying coil placed in a uniform magnetic field? The currents in the two sides of the forces are at right angles to the magnetic field lines, so there will be forces on them. One force is up an the other down because the currents in the two sides of the coil are in opposite directions. The effect of these forces is to make the coil rotate. What can the motor effect be used to produce? Continuous rotation of the coil, by using a commutator to ensure that the direction of the current in the coil is reversed at an appropriate point in each rotation. How does a commutator work? It is fixed to the coil and rotates with it. Ad the coil rotates, each half of the split ring touches one brush for half a turn, and the other brush for the next. So the current direction in the coil is reversed twice every turn - changing the direction of the magnetic forces, and keeping the coil rotating.

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