Flashcards in Physics Summary Deck (52):
How do you calculate speed from a distance speed time graph?
The gradient is change in distance (vertical axis) divided by the change in time (horizontal axis)
Important notes about distance time graphs.
Flat sections is where it's stationary
Straight uphill or downhill sections means traveling at steady speed.
The steeper the graph the faster it's going.
Downhill sections means it is returning to its starting point.
Curves represent accelerating or deceleration.
A steeping curve means its speeding up (increasing gradient)
A levelling off curve means it's slowing down (decreasing gradient)
Important things about velocity time graphs
Flat sections represent steady speed.
The steeper the graph the greater the acceleration or deceleration.
Uphill sections (/) are acceleration
Downhill sections (\) are deceleration.
The area under any section of the graph (or all of it) is equal to distance traveled in that time interval.
A curve means changing acceleration.
Calculating acceleration velocity and alfi stance from a velocity time graph
Acceleration =gradient =vertical change/horizontal change
The velocity at any point is simply found by reading the value off the velocity axis.
The distance traveled in any time interval is equal to the area under the graph.
Calculating speed from a distance time graph
Calculating speed from a distance time graph -it's just the gradient
Speed =gradient =vertical /horizontal
What is the difference between speed and velocity.
Speed is just how fast you're going (e.g 30mph or 20m/s) with no regard for direction.
Velocity however must also have the direction specified e.g 30mph North or 20m/s, 060 degrees
Explain the difference between mass and weight?
Mass is just the amount of stuff in an object. Kg
Weight is caused by the pull of gravitational force. Neutons
What is terminal velocity?
When an object reaches it's maximum speed.
It depends on their shape and area.
What are two different parts of the overall stopping distance of a car?
Thinking and Braking distances.
What is the formula that relates to the force on a spring and it's extension?
F = K x e
Force = spring constant(N per metre) x Extension.
What is the advantage of using regenerative braking systems?
Slow the car down quicker.
Converts kinetic energy into electric energy using the motor.
Stored as chemical energy in the motor's battery.
Explain how seat belts, crumple zones, side impact bars and air bags are useful in a crash.
Crumple zones increase the impact time, decreasing the force produced by the change in momentum - at the front and the back of the car crumple up at impact.
Side impact bars are strong metal tubes fitted into car door panels. They direct the kinetic energy of the crash away from the passengers to other areas of the car such as crumple zones.
Seat belts stretch slightly, increasing the time taken for the wearer to stop. This reduces the forces acting on the chest. Some of the kinetic energy of the wearer is absorbed by the seat belt stretching.
Air bags slow you down gradually and prevent you from hitting hard surfaces in the car.
What causes the build up of static electricity? Which particles move when static builds up?
It is caused by friction when insulating materials are rubbed together. They leave a positive static charge on one, and a negative static charge on the other.
Only electrons move, never the positive charges.
Explain how resistance of a component changes with it's temperature and turns of ions and electrons.
The greater the resistance across a component the smaller the current that flows. A higher temperature gives the ions more energy making the electrons flow slower as it's harder to get through.
Give three applications of LEDs.
Lights, digital clock, remotes.
Describe how the resistance of an LDR are varies with light intensity. Give and application of an LDR.
An LDR is a resistor that is dependent on the intensity of light.
In bright light resistance falls
In darkness the resistance is highest
They have lots of applications including automatic night lights, outdoor lighting and burglar detectors.
Name three wires in a three core cable.
Earth =yellow and green
Neutral = blue
Three pin plug
Neutral on left bottom
Live bottom right
Earth is Middle
Explain fully have a fuse and an earth wire work together.
Earthing and fuses preventelectrical overloads.
If there is a fault and the livewire touches the metal case the earth wire carries the XS charge to prevent electrocution.
A surgeon current melts the fuse or trips the circuit breaker in the live wire when the amount of current is greater than the fuse rating. This cuts off the life supply and breaks the circuit.
Isolates the whole appliance make it impossible to get an electric shock.
How dose an RCCB stop you from getting electrocuted?
Residual current circuit breakers. The text the difference in current and cuts of the power by opening the switch. Operates faster than fuses which makes them safer. Work for small current changes that might not be large enough to melt a fuse and this means that they are more effective at protecting against electrocution.
Explain how the experiments of Rutherford and Marsden led to the nuclear of the atom?
In 1909 Rutherford and Marsden try firing a beam of alpha particles at gold foil. Because of the plum pudding model they expected the positively charged alpha particles would be slightly deflected by the electrons.however most of the Alpha particles just went straight through, the old one came back at them which made them realise that most of the mass of the atom is concentrated in the centre in a teeny nucleus.
What is half life?
Half life is the average time it takes for the number of nucli in a radioactive isotope sample to half.
2 Neutrons + 2 protons (helium nuclus)
Highly ionising – knocks off electrons. Not very penetrating
blocked by: skin, paper,several centimetres are air.
You used in smoke detectors. A week source of alpha radiation is placed in the detector, close to 2 electrodes. The social causes ionisation and the current flows between the electrodes. If there is a fire then smoke will it is over the radiation causing the current to stop and the alarm sound.
Affected by electric and magnetic fields because it carries a 2+ charge
High energy and high speed electrons. Moderately ionising moderately penetrating blocked by:several centimetres of aluminium. Affected by electric and magnetic fields because they carry charge negative.
Used in medical chases and paper thickness
Blocked by: thick lead, very thick concrete.
Used for radiotherapy and sterilisation of food and surgical instruments.
The splitting up of big atomic nuclei.
Happens in nuclear power stations.
What has to happen for nuclear fission to happen?
Slow moving neutron absorbed into 235 uranium or 239 plutonium. Which makes nucleus unstable causing it to split.
Each split causes two or three neutrons which hit other nuclei which causes a chain reaction.
Joining of 2 atomic nuclei to form a larger one.
Fusion in more detail
Fusion release a lot of energy more than fission.
Happens in stars =process by which energy released in stars.
Not much radioactive waste unlike fission.
Plenty of hydrogen for fuel.
Only happens at really hight temperatures-10000000c
Caused by the movement of electrons. Caused by 2 insulators rubbing together and transferring electrons
+ve and -ve electrostatic charges are caused by the movement on electrons.
Positive electrostatic charges are caused by...
Loss of electrons
Positive and negative
- - repell
What impacts the voltage of an insulator object?
The greater the charge of an insulator object the greater the voltage between it and the earth.
What is a current
An electric current is the flow of electrons. Rate of flow of charge -amps
Electrons go from negative to positive
The difference in energy between two point
Is the measure in voltage and is how big the push on electrons.
Anything that resists an electric current. Measured in ohms
Current same at any point
Voltage splits up over each component
Potential difference is the sum of the resistance of each component.volts shared across bulbs. Total potential difference (voltage) is shared between components.
The current splits up down each 'stand'
Voltage the same across each 'stand'
The current has a choice of routs
Potential difference is same anywhere in circuit.
Total current through whole circuit is the sum of the current through separate components.
Voltage =potential difference
Current -voltage graphs
Current increases in proportion to voltage which obeys ohms law.
Current - voltage graphs
As voltage increase the bulb gets hotter and resistance increase.
Higher resistance =slower current
Doesn't obey ohms law
Current - voltage graphs
A diode only lets current go in one direction - very high resistance in other direction.
Current flowing in other direction.
Direct current -current only flows in one direction
Stands for alternating current - the current changes direction 59 times every second (frequency = 50HZ)
Produces a graph of potential difference against time.
Declared voltage = 0.7 x peak voltage
In uk it is 230v
Peak voltage = 230/0.7
The period of an AC supply is the time taken for one complete oscillation. You can fined this by looking at the time between one peak and the next or trough to trough. Between any two identical places on adjacent oscillations.
Frequency = 1/period
Residual current circuit breakers
Works on comparing two electromagnets
Detects difference in current between the live wire and neutral wire.
Safety device - alternative to fuse. Works on electromagnets - 2 of them. Detects dif fences in current between the live wire and neutral. Quicker than fuse and easier to reset
Always used of an appliance has a metal case. If there is a fault in the appliance causing the live wire to touch the case the current "surges"down the earth wire and fuse blows.
Symbol a small rectangle inside a bigger one.
Some appliances such as vacuum cleaners have double insulation because they do not have an Earth wire.