# P2

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What is the velocity of an object?
Its speed in a given direction, if an direction it changes velocity even if the speed stays the same + increase in velocity = acceleration. Negative acceleration = deceleration (object is slowing down).
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What can a velocity-time graph show?
Acceleration given by gradient. Distance travelled is shown by calculating the area of the shape beneath the gradient. If the line is horizontal then the acceleration is 0 and the object is moving at a steady pace. Negative gradient = deceleration.
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What can a distance-time graph show?
Speed given by gradient. The steeper the grad, the greater the speed. Constant speed = straight line that slopes upwards. Stationary = horizontal line.
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What are action and reaction forces and how can they be applied?
Objects always exert equal and opposite forces on each other. i.e is a car is being driven forwards, there is a force from the tyre on the ground pushing backwards. If you place a book on the table, the table will exert eq+opp forces upwards on the b
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What is resultant force and what happens when the resultant force is zero?
The single force that would have the same effect on the object as all of the original forces acting together. When at zero: if the objects at rest, it will stay at rest or if the object is moving, it will carry on moving at the same speed + direction
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What does it mean when the resultant force of an object is not at zero?
There will be an acceleration in the direction of the force. A resultant force always causes an acceleration and is needed to make an object change direction. The greater the resultant force on an object, the greater its acceleration.
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What affects the braking force needed?
The faster the speed of a vehicle, the bigger the deceleration needed to stop it in a particular distance = bigger the braking force needed.
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What is the stopping distance and what can affect it?
The distance travelled during the driver’s reaction time (thinking distance) plus the distance it travels under the braking force (braking distance).
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What can affect the thinking + braking distance?
Reaction time is increased if the driver is tired or under the influence of alcohol/drugs. Braking distance affected by poorly maintained roads/adverse weather conditions + Condition of the car i.e. worn tyres/brakes will increase it.
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What is the resultant force acting on an object that fall freely?
Gravity (will make object falling near earth’s surface accelerate at 10m/s2). Force of gravity is called weight and the acceleration = acceleration due to gravity (W = m × g).
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What happens when an object falls through a fluid?
Fluid exerts a drag force on the object resisting its motion. Faster the object falls, bigger the drag force becomes until its equal to the weight of the object. Resultant force is now 0 so object stops accelerating + moves at terminal velocity (cons
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What is an elastic object?
One that regains its original shape when the forces deforming it are removed i.e. when weights are hung from a spring the increase in length from the original is called an extension.
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What do we obtain when we plot a graph of extension against force applied for a spring?
A straight line that passes through the origin which tells us that the extension is directly proportional to the force applied. If we apply too big a force the line begins to curve because we have exceeded the limit of proportionality.
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What does Hooke’s law state?
That the extension is directly proportional to the force applied provided the limit of proportionality isn’t exceeded. F = k × e
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What happens when a string is stretched (in terms of energy)?
When an elastic object is stretched, work is done and stored as EPE (elastic potential) in the object, when the stretching force is removed this stored energy is released. The stiffer a spring is, the greater its spring constant.
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What is fuel economy and how can we improve fuel economy?
Reducing the speed of a vehicle reduces the amount of fuel used. Reducing the air resistance by making the vehicle more streamlined (i.e. fitting a wind deflector) also improves fuel economy.
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Why are speed cameras used?
To discourage motorists from speeding as they can determine the speed of a motorist at a particular point. Motorists caught speeding are fined and may lose their license.
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When does skidding happen?
When the brakes on a vehicle are applied too harshly. When a vehicle skids, the wheels lock and slide along the road surface, increasing the stopping distance.
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How can skidding be reduced?
By using anti-skid surfaces that are rougher than road surfaces, increasing the friction between the vehicle tyres and the road. They are used in places where drivers are likely to brake i.e. near traffic lights/road junctions.
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What happens when an object starts to move?
A force must have been applied to it – energy is transferred and work is done. When work is done moving the object, the supplied energy is transferred
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What happens when two electrically insulating materials are rubbed together?
Electrons are rubbed off one material on deposited on the other. As electron have a negative charge the material that has gained electrons becomes negatively charged + the one that has lost electrons becomes positively charged.
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What happens if two negatively charged objects are brought close together?
Oppositely charged objects attract, same charged objects repel. The bigger distance between the objects, the weaker the force between them.
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How is current and potential difference measured?
Ammeters measure current (amps) + are always placed in series with the component. Voltmeters measure pd + are always placed in parallel with the component.
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What is resistance?
Opposition to current flow in ohms. R = V / I
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What is Ohms Law?
When the current is directly proportional to the voltage across a resistor. Any component that obeys this it is an Ohmic conductor.
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Describe the current potential graph for a filament light bulb.
Not directly proportional. The resistance of the filament increases as the current increases because the temperature also increases. Reversing the Pd makes no difference to the curve. Current is the rate of flow of charge.
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Describe the current potential graph for a diode.
It is not directly proportional. It only flows in one direction because there is a large resistance in the other direction so the current is zero.
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Describe the resistance of light dependent resistors and thermistors.
As the light falling on it gets brighter, the resistance of an LDR decreases. As the temperature goes up, the resistance of a thermistor foes down.
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Describe a series circuit.
Components are connected one after another, so if there’s a break anywhere in the circuit the charge stops flowing. The current is the same in each component as there is no choice of route for the charge.
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How could you find the potential differences and resistances of the components?
Supply of pd shared between components. Resistances of the components add up to give the total resistance of the circuit. The bigger the resistance of a component, the bigger its share of pd.
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Describe a parallel circuit.
Each component is connected across the supply, so it there is a break in one part of the circuit, charge can still flow in the other parts.
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Describe the share of current and potential differences in parallel circuits.
As there are junctions in the circuit, different amounts of charge can flow through different components. The bigger the resistance, the bigger the smaller the current through it. Pd across each component is the same.
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What is direct current and alternating current?
D.C. – Cells/batteries supply current that passes round the circuit in one direction. A.C. – the current form the mains supply passes in one direction, then reverses and passes in the other direction.
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Describe the mains supply
The frequency of the UK mains supply is 50 Hertz (Hz) which means it changed direction 50 times per second. Mains voltage is 230 V.
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Describe the live wire of the mains supply.
The live wire of the mains alternates between a positive potential (peak voltage of +325V) & a negative potential (peak voltage of -325V) with respect to the neutral wire which stays at 0 volts.
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Why are certain parts of plugs made out of certain materials>
Outer cover made of plastic/rubber (good electrical insulator). Pins made of brass (good electrical conductor, hard, resistant to corrosion).
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Why don’t appliances with a plastic case need to be earthed?
Appliances with plastic cases do not need to be earthed as they are ‘double insulated’ + connected to 2-core cable containing only a live + neutral wire. Plastic is an insulator and cannot become live.
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Why do appliances with a metal cases need to be earthed?
As if a fault develops + the live wire touches the metal case, the case becomes live and could give a shock to anyone who touches it.
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What is the purpose of a fuse?
Always fitted in series with the live wire and cuts the appliance off from the from the live wire if the fuse blows
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How does a fuse work?
If a fault develops in an earthed appliance, a large current flows to earth and melts the fuse, disconnecting the supply.
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What does the rating of a fuse depend on?
The rating of a fuse should be slightly higher than the normal working current of the appliance. If its much higher it won’t melt soon enough, if it isn’t higher.
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What is the difference between a circuit breaker and RCCB (Residual Current breaker)?
A circuit breaker is an electromagnetic fuse that opens and cuts of the supply if the current is bigger than a certain value whereas an RCCB cuts off the current in the live wire is it is different to the current in the neutral wire (faster).
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What is power?
The rate at which an electrical appliance transfers energy into other forms of energy.
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What should be taken into account when using and buying electrical appliances?
Avoid overloading sockets as they may cause overheating and a risk of fire and never use in a bathroom/with wet hands. Cost effectiveness i.e. Filament/halogen light bulbs are less efficient than low-energy light bulbs + don’t last as long.
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How do the nuclei of radioactive substances become stable and list the three different types of radiation emitted as a result?
As the nuclei of radioactive substances are unstable, they become stable by radioactive decay emitting either alpha, beta or gamma radiation to turn into other elements. This is random + unaffected by external factors.
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What is background radiation?
Radiation that is around us all the time from radioactive substances in the environment, space + devices (i.e. X-ray tubes).
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What was the plum pudding model?
An older theory regarding the model of an atom – Scientists used to believe that atoms consisted of spheres of positive charge with electrons stuck to them like plums in a pudding.
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What did the alpha particle scattering experiment in which Geiger, Marsden + Rutherford fired alpha particles at thin gold foil suggest?
Most of the atoms passed through the foil (most of the atom is empty space). Some of the alpha particles were deflected through small angles (nucleus had a pos charge) + a few rebound through large angles (nucleus = large + pos).
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What is the change in the nucleus and the particle emitted in alpha decay?
Nucleus loses 2 protons + 2 neutrons. 2 protons + 2 neutrons are emitted as an a particle. The atomic number goes down by 2 + the mass number goes down by 4.
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What is the change in the nucleus and the particle emitted in beta decay?
A neutron in the nucleus changes into a proto and an electron. The electron created in the nucleus is instantly emitted. The atomic number goes up by 1 + the mass number stays the same.
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What happens when a nucleus emits gamma radiation?
There is no change in the atomic number or the mass number. A gamma ray is an electromagnetic wave released from the nucleus with no charge or mass.
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Describe an alpha particle and what it can be stopped by.
Relatively large (has lots of collisions with atoms), strongly ionising + don’t penetrate far into a material, positive charge + are deflected by electric + magnetic fields. They can be stopped by a thin sheet paper/human skin/few cm of air.
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Describe beta particles.
Much smaller + faster than a particles so are less ionising, penetrate further, have a negative charge + are deflected by electric + magnetic fields in the opposite direction to a particles. Blocked by a few metres of air/thin sheet of aluminium.
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Describe gamma rays.
Electromagnetic waves that will travel far into the material before colliding with an atom. Weakly ionising, very penetrating, not deflected by electric/magnetic fields + are blocked by several cm of lead/ metres of concrete are needed to absorb most
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What happens to the count rate of a radioactive sample over time?
It decreases over time and depends on the isotope. The count rate measures the radioactivity of a sample of a radioactive material.
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What is the idea of a half-life used for?
To measure how quickly the radioactivity decreases. It is the time taken for the count rate from the original isotope to fall to half its initial value (time taken for the number of unstable nuclei ina sample to halve.
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## Other cards in this set

### Card 2

#### Front

What can a velocity-time graph show?

#### Back

Acceleration given by gradient. Distance travelled is shown by calculating the area of the shape beneath the gradient. If the line is horizontal then the acceleration is 0 and the object is moving at a steady pace. Negative gradient = deceleration.

### Card 3

#### Front

What can a distance-time graph show?

### Card 4

#### Front

What are action and reaction forces and how can they be applied?

### Card 5

#### Front

What is resultant force and what happens when the resultant force is zero?