# Higher: Physics

## Revision Cards for the SQA Higher Physics Course

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425 questions

🇬🇧 | 🇬🇧 |

What is the formula for frequency | F=1/T f is frequency in Hz T is period in seconds |

What are the two types of current | Direct current alternating current |

Describe direct current | The electrons flow in one direction through a conductor |

Describe alternating current | Current that changes direction and instantaneous value with time |

Give examples of sources direct current is produced by | Chemical cells batteries |

Give examples of sources alternating current is produced by | Mains electricity |

What is meant by peak current | The maximum value of current |

What is meant by peak voltage | Maximum value for potential difference |

What is an r.m.s value? | Root means square the alternating current equivalent of a direct current supply |

What is the formula for peak/rms current | Irms=Ipeak/√2 |

What is the formula for peak/rms voltage | Vrms=Vpeak/√2 |

What does the time base setting on an oscilloscope tell us | The number of milliseconds it takes the trace to cross each box from left to right |

What does voltage gain setting on an oscilloscope tell us | The number of volts each box represents in the vertical direction |

What is the formula for frequency | F=1/T f is frequency in Hz T is period in seconds |

Describe voltage in a series circuit | Voltages in a series circuit combine to give the supply voltage |

Describe voltage in a parallel circuit | Voltage across branches is the same |

Describe current in a series circuit | Current is the same at all points |

Describe current in a parallel circuit | Currents in parallel branches combine to give the supply current |

What are potential divider circuits | Circuits in which voltage is split between two components |

What is a wheatstone bridge circuit | A circuit where two potential divider circuits are connected in parallel |

What are potential divider circuits used for | To provide a specific voltage to a component |

How do you calculate the voltage across the voltmeter in a wheatstone bridge | Look at the terminals of the battery to identify which way current flows calculate the voltage across the two resistors that current first passes through (use potential divider formula or ratios) find the difference between the two voltages |

What does it mean when the voltmeter on a wheatstone bridge reads 0? | The wheatstone bridge is balanced r1/r2=r3/r4 |

What is e.m.f | Electromotive force the voltage measured across the terminals of supply when no current is being drawn |

What is internal resistance | The resistance of the material that makes up a cell |

What is the symbol for internal resistance | R (small r) |

What is an ideal supply | An electrical supply that has no internal resistance |

What is meant by lost volts | The potential difference across the internal resistance |

What is t.p.d | Terminal potential difference the energy transferred to each coulomb of charge passing through the supply when a current is being drawn |

What is the formula for e.m.f | E.m.f = t.p.d + Ir |

What is the formula for lost volts | Lost volts = Ir |

What is the relationship between t.p.d and current | As current increases, t.p.d decreases |

When do you get maximum terminal potential difference in a cell | When current is 0 |

When there are no lost volts in a cell what happens to t.p.d | It becomes equal to the e.m.f of the battery |

How do you find the e.m.f of a battery from a t.p.d against current graph | Find the y intercept |

What is an open circuit | A circuit where there is no current flowing |

What is meant by short circuit | When two wires connect directly across a component and the current flows through the short rather than through the component |

What is the resistance of a short circuit | Zero or very little |

What is short circuit current | The maximum current a battery can deliver when external resistance of the circuit is zero |

How do you find the internal resistance from a voltage against current graph | Take the negative of the gradient |

What are capacitors | Devices that can store charge and energy in a DC circuit |

What is the formula for capacitance | C=Q/V C is capacitance in farads (F) Q is charge in coulombs (C) V is voltage in volts (V) |

What will a graph of charge stored on a capacitor against voltage produce | A straight line through the origin |

What is the relationship between charge stored on a capacitor and potential difference | Charge is directly proportional to potential difference |

What is the gradient on a charge stored on a capacitor against potential difference graph | Capacitance |

What is the area under the graph on a charge-potential difference graph | Energy stored in a capacitor |

What are the formulas for energy stored in a capacitor? | E=1/2QV E=1/2CV^2 E=1/2Q^2/C |

Describe what happens to current as a capacitor charges | When capacitor is uncharged initially, electrons flow freely to capacitor so current is large as electrons build on one plate of the capacitor they exert a repulsive force on electrons coming on to the capacitor, reducing rate of flow of electrons current decreases and eventually drops to zero when the capacitor is fully charged |

Under what conditions only does current flow to a capacitor | When there is a potential difference between the supply and the capacitor |

What happens to current when the potential difference across the capacitor is the same as the supply | No more current flows |

What is the maximum voltage across a capacitor equal to | The voltage across the supply |

Describe what happens to potential difference as capacitor charges | Current only flows when there is a potential difference between the supply and the capacitor when the potential difference across the capacitor is the same as the supply, no more current flows |

What is the effect of resistance on time it takes for a capacitor to charge | The higher the resistance, the longer the capacitor will take to become fully charge |

What is the effect on capacitance of a capacitor on time it takes to charge | The higher the capacitance of the capacitor the longer it will take to charge higher capacitance can hold more coulombs of cha |

What is a conductor | A material that allows the flow of electricity through it |

What is an insulator | A material that does now allow electrons to easily move through it |

What is a semi conductor | Materials that can act as conductors or insulators under certain conditions |

How do individual atoms conduct | In conductors the outer energy level is not full this allows a degree of movement for the electrons |

Why don't individual atoms of an insulator conduct | In an insulator the outer energy level is full and the electrons are not free to move |

What happens to the energy levels of atoms when they are brought together | The outer energy levels interact with each other to form an energy band |

What is the conduction band | The highest energy band |

What is the valence band | The band below the conduction band |

What is a band gap | Space between energy bands |

Describe the energy bands in conductors | Valence and conduction band overlap and are both partially filled valence electrons can move freely through the material |

In insulators how full is the valence band | Completely full of electrons |

Why don't insulators conduct electricity | At room temperature there is not enough energy to move electrons from the valence band to the conduction band |

How full is the valence band in semi conductors | Completely full |

What is the size of the band gap in semi conductors | Relatively small |

What happens when you increase the temperature of a semi conductor | Electrons are given enough energy to jump the band gap to from the valence band to the conduction band, and so the material conducts |

Explain using band theory why a semiconductor can conduct at room temperature | The band gap in semi conductors is small some electrons have enough energy to move from the valence band to the conduction band |

What are most semi conductors made out of | Elements with four outer electrons eg. silicon |

What is the structure of bonded atoms with 4 outer electrons | They form a crystal lattice structure where each electron is bonded to another (no free electrons) |

What happens if you introduce an atom with 5 outer electrons into a semi conductor | There will still be a lattice structure but one atom will have an additional electron |

What can the extra electron in n type semi conductors do | Displace electrons from silicon atoms these electrons can in turn displace other electrons |

What happens when an atom of valency three is added to a semi conductor | There is a missing electron in the lattice so this leaves a hole |

What is the name of semi conductors where a valence 3 atom has been introduced | P-type semi conductor |

Why do p-type semi conductors conduct | The hole appears to move due to electrons moving in the opposite direction, causing the material to conduct |

What is doping | The adding of impurities to pure silicon to produce n-type or p-type silicon |

What effect does doping have on the elctrical properties of semi conductors | It increases their conductivity, hence reducing their resistance |

What is a p-n junction | When n type and p type semi conductors are combined one half of the semi conductor is made of p type material, and the other half n-type material |

What is a depletion layer | A region where excess holes from the p type material combine with excess electrons from the n type material (the charges combine) |

At a p-n junction what is the charge of the n-type side | There is a region of positive charge on the n type side |

At a p-n junction what is the charge of the p type side | There is a region of negative charge on the p type side |

What is reverse bias | When a positive voltage is applied to the n type side and a negative voltage is applied to the p type side of the material |

What is the effect of reverse bias on the size of the depletion layer | Size of depletion layer increases |