4371439
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Flashcards by Will Welford, updated more than 1 year ago
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| Question | Answer |
| Define: conservation of momentum | In any collision or explosion, total momentum remains constant provided no external forces act. |
| Define: elastic collision | No kinetic energy is lost |
| How are force and momentum related? | Force = rate of change of momentum |
| What is meant by 'impulse'? | The product of force and time |
| Define the term 'radian' | 1 radian is the angle subtended by a circle of radius r by an arc of length r |
| Define: angular speed | The angle in radians turned through in 1s |
| Give 3 factors that affect centripetal force | mass speed radius (of circle) |
| What conditions must be satisfied for an object to be in SHM? | 1. The acceleration of the object is proportional to its displacement from the equilibrium position. 2. The acceleration is always directed back towards the equilibrium position. |
| Energy in SHM is the interchange between which two energy forms | Kinetic and potential |
| How is the oscillations of a simple pendulum and a mass-spring system affected if taken to the Moon? | simple pendulum - longer time period mass-spring - no effect |
| What is a free vibration? | System displaced and left to oscillate at its natural frequency |
| What is a forced vibration? | System driven at frequency other than natural frequency |
| What happens when a system is driven at its natural frequency? | Resonance Amplitude of oscillations increases |
| What is damping? | Resistive force that causes amplitude of oscillations to decrease |
| What is critical damping? | System returns to equilibrium as quickly as possible without 'overshooting' |
| State Newton's gravitational law | Gravity is an attractive force between point masses that is proportional to the product of the two masses and inversely proportional to the square of the distance between them |
| What do gravitational field lines show? | The direction a small test mass would move when placed in the gravitational field |
| Describe in one word the gravitational field around a planet | Radial (inwards) |
| What is an equipotential? | A region / surface of constant potential |
| Define: gravitational field strength | The force per unit mass acting on a small test mass placed in a gravitational field |
| Define: gravitational potential | The energy required to bring a unit mass from infinity to some point in a gravitational field, this is work done by gravity |
| Why is gravitational potential a negative value? | Work is done to reach infinity at which point gravitational potential is zero |
| What is the gradient of a gravitational potential vs. distance graph equal to? | Gravitational field strength |
| Define: electric field strength | The force per unit charge acting on a small positive charge at that point |
| What is the unit for electric field strength? | Newton per Coulomb or Volt per metre |
| What is the unit for gravitational field strength? | N / kg |
| Define: electric potential | The work done in bringing a unit positive charge from infinity to that point |
| How do you find the electric potential difference between two points in an electric field? | The work done in moving a unit positive charge from the point at the lower potential to that at the higher potential |
| What is the unit for electric potential difference? | Volt, V |
| What is the electric field strength equal to in a uniform field? | E = V / d |
| What is the force F on a charge q equal to in an electric field of field strength E? | F = qE = qV / d |
| Describe the motion of a charged particle entering a uniform electric field perpendicular to the field lines | parabolic |
| Give one difference between electric and gravitational fields | Act on charges instead of masses or Can be attractive or repulsive, g fields are only attractive |
| Define capacitance | charge stored / potential difference |
| Define the Farad, F | 1 Coulomb stored when a p.d. of 1 Volt is applied |
| What does the area under of a graph of Q against V represent? | Energy stored |
| What does the gradient of a graph of Q against V represent? | Capacitance |
| What is the time constant of a capacitor equal to? | RC |
| After how many time constants is a capacitor considered to be charged or discharged? | 5 |
| Define: magnetic flux density | Force per unit current per unit length |
| Fleming's left hand rule: State what the 3 fingers represent | First finger: B field Second finger: Current Thumb: Force |
| Fleming's right hand rule: State what the 3 fingers represent | First finger: B field Second finger: Current Thumb: Force |
| Why does a particle moving in a circular path not spiral inwards? | Force is perpendicular to the velocity at any time The force causes a change in direction, but not a change in the magnitude of the velocity No work is done in the direction of the force |
| State Lenz's law | The direction of the induced EMF is such that the current it causes to flow opposes the change which causes it |
| Define: magnetic flux and state the unit | Product of B and A Webers, Wb |
| Define: magnetic flux linkage and state the unit | Product of the number of turns on a coil and the magnetic flux (NBA) Unit: Weber-turns |
| How is the induced EMF and the flux linkage related? | Rate of change of flux linkage = magnitude of induced EMF |
| Describe how a p.d. is induced across the secondary coil of a transformer | An alternating p.d. across the primary coil produces an alternating magnetic field in the iron core. This is linked to the secondary coil. An alternating p.d. is induced across the secondary coil. |
| Describe how the efficiency of a transformer is maximised. | The core is made from iron which can be magnetised and de-magnetised quickly. The core is laminated, reducing eddy currents. Low resistance wire is used for the coils, reducing the heating effect of the current. |
| Why is electricity transmitted at high potential differences? | High p.d. means low current. Low current means less energy transferred to the surroundings, increasing efficiency |
| What is heavy damping? | No oscillating motion occurs and the object returns to equilibrium a lot slower than if critically damped |
| What is light damping? | The time period of the oscillations do not change but their amplitude decreases over time |
| Newtons First Law of Motion | An object remains at rest or in equilibrium unless acted on by a force |
| Newtons Second Law of Motion | The rate of change of momentum of an object is proportional to the resultant force on it. |
| Newtons Third Law of Motion | When two objects interact they exert an equal and opposite force on the other |
| Define: totally and partially Inelastic collisions | Totally = The colliding objects stick together Partially = colliding objects move apart and have less kinetic energy then before the collision |
| Define: angular displacement | The angle an object in circular motion turns through |
| Equation for force on a car over a hill | mg-S=mv^2/r |
| Equation for friction on the tyres of a car going round a roundabout | F=mv^2/r |
| Equation to determine the maximum speed a car can travel round a roundabout without slipping | Limiting force of Friction = mass x maximum velocity squared / radius |
| What equation give the speed of a car on a banked track without sideways friction | v^2 = gr tan(x) |
| The long swings equation for maximum speed and the centripetal force | Maximum speed squared = 2gh S-mg = mv^2 / L |
| The frequency of an oscillating spring-mass system is reduced by: | 1) Adding extra mass 2) Using weaker springs |
| Define: Resonance | the amplitude of vibration of an oscillating system subjected to a periodic force is largest when the periodic force has the same frequency as the natural frequency of the system |
| What is the difference between a uniform and radial field? | Radial fields are represented by lines that appear like the spokes of a wheel. The magnitude of g decreases with increased distance from the massive body Uniform fields are parallel lines. g is the same direction and magnitude throughout |
| Define: potential gradient | The change of potential per metre at that point. |
| Define: Kepler's Third Law | r^3/T^2 is the same for all planets |
| Properties of Geostationary satellites | Orbits directly above the equator Same direction of motion at the earth same time period as the earth |
| What is the negative of the electric field strength? | potential gradient |
| Define: Coulombs Law | For two point charges at distance, r, apart; the force between the two charges is given by the equation F=Q1Q2/4Pi(permittivity of free space)r^2 |
| Capacitor uses | 1) Smoothing circuits (smoothing unwanted variation in voltage) 2) Back-up power supplies 3)timing circuits 4) tuning circuits 5) filter circuits |
| Define: The motor effect | A current-carrying wire placed at a non-zero angle to the lines of force of an external magnetic field experiences a force perpendicular to the wire due to the field. |
| How is induced EMF increased | Moving the wire faster. using a stronger magnet. making the wire into a coil and moving the magnet in and out of the coil. |
| How can EMF be induced | 1) a wire cutting a magnetic field perpendicular to the field lines 2) using an electric motor in reverse 3) Using a cycle dynamo |
| Which end of the magnet does the current flow clockwise around? | South. CouNterclockwise round the North |
| Define Faraday's Law | The induced EMF in a circuit is equal to the rate of change of flux linkage through the circuit |
| On a graph of flux linkage against time - What does the gradient represent? | The change of flux linkage per second, which represents the induced EMF |
| What is the difference between a step-up and step-down transformer | Step-up) More turns on the secondary coil than the primary coil Step-down) Fewer turns on the secondary coil than the primary coil |
| What is the current in the secondary coil divided by the current in the primary coil equal to | 1) the Voltage in the primary coil divided by the voltage in the secondary coil 2) the number of turns in the primary coil divided by the number of turns in the secondary coil |
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