Physics 2 (Year 11) Flashcards
What is a voltmeter and how is it connected in a circuit?
A voltmeter is a device for measuring VOLTAGE.
Voltage is measured in VOLTS.
(Do not say a voltmeter measures volts - this is wrong)
A voltmeter is connected as shown below
What is an ammeter and how is it connected in a circuit
An ammeter measures CURRENT
Current is measured in AMPS.
(Do not say that an ammeter measures amps)
What are the circuit symbols for:
a) A resistor
b) A bulb
c) A power supply
Describe the difference between components arranged in series and in parallel.
In series (one branch):
- The current through all the components is the same.
- The voltages of all the components added together equals the voltage of the battery.
- The components might not each have the same voltage across them (the amount of voltage across them will depend on their resistances)
- Advantage of series circuits is that all components have the same current.
In parallel (multiple branches)
- The current will be the same for components in the same branch. But different branches may have different currents
- The voltages for objects on the same branch may be different. But all branches will have the same total voltage.
- Advantage of parallel circuits is that if a component breaks, the other components on different branches will still work normally.
How would you test the relationship between current and voltage for a component. Include a circuit diagram in your answer.
The circuit diagram needed is shown below. The procedure is as follows:
- Measure the current through the component using an ammeter, and the voltage across the component using a voltmeter.
- Use the variable resistor to change the resistance in the circuit - and therefore the current.
- Measure the current and voltage through the component again.
- Plot a graph of your results with current on the x axis and voltage on the y axis.
- The gradient of the line is the resistance of the component being tested.
Draw a graph of current against voltage for:
a) a resistor.
b) a filament lamp.
c) a diode.
(remember, because on these graphs voltage is on the x-axis, the gradient is 1/resistance).
Interpret distance time graphs correctly.
Remember that for distance-time graphs the gradient of the line will tell you the velocity
Interpret velocity-time graphs correctly.
Remember that for a velocity time graph the area under the graph is the distance travelled.
State Newton’s first law.
Bodies remain stationary, or continue to travel in a straight line, unless acted upon by a resultant force.
State and explain newtons second law.
The applied force on a body is proportional to the rate of change of momentum.
Explain the factors which affect the acceleration of a body.
The two factors that affect the acceleration of a body are its mass, and the force applied to it.
Acceleration is proportional to resultant force, and inversely proportional to a bodies mass.
Explain the difference between weight and mass.
Mass is how much stuff an object is made from and is measured in kg.
Weight is how much force that mass presses down on the Earth with and is measured in Newtons.
Weight = Mass x Acceleration due to Gravity
(The acceleration due to gravity on Earth is 10N/kg)
Explain how the forces, acceleration and velocity of a skydiver change throughout a fall.
At the moment of jumping
The skydiver has not started moving downward yet so there is no upward force. Gravity is pulling the skydiver down. This means that the resultant force is maximum and so is the acceleration.
After a couple of seconds
As the skydivers speed increases so does the air resistance - but the weight of the skydiver remains constant. At this point the skydiver is still accelerating, but not at as high a rate as before, because the resultant force is not as large.
After a while
Eventually the skydiver is traveling so fast that the drag is equal to the weight of the skydiver. Because of this the resultant force is zero. As there is no resultant force there is no aceleration - the skydiver cannot go any faster so we say he is at terminal velocity
State Newton’s third law.
In an interaction between 2 bodies, A and B, the force
exerted by body A on body B is equal and opposite to
the force exerted by body B on body A. The forces are of the same type.
Explain what happens when a force acts on a body in terms of energy transferred.
When a force acts on a body, if the body moves in the direction of the force work is being done (energy is being transferred). The total amount of energy remains constant.
Examples of this are friction acting on a rolling ball: (kinetic energy of the ball -> heat energy)
Another exampe is a man falling from an aeroplane (gravitational potential energy -> Kinetic Energy)
A third example is an object falling at terminal velocity (Gravitational potential -> Heat energy)
Define work done.
Work done is a measurement of the energy transferred.
Define thinking distance
The distance travelled by a vehicle from the moment when a hazard is first spotted, to the moment that the brakes are first applied.
(Note: This is similar to reaction time except that it is the DISTANCE travelled while reacting)
Define braking distance.
The distance travelled from the moment when the brakes are first applied to the moment when the vehicle comes to a complete stop.
Define stopping distance
The distance travelled from the moment when a hazard is first spotted to the moment when the vehicle comes to a complete stop.
Stopping distance = Thinking Distance + Braking Distane
State factors which effect:
a) thinking distance.
b) breaking distance.
Thinking Distance
Drugs (both legal and illegal), tiredness, age, speed.
Breaking Distance
Condition of tyres/brakes, condition of the road, speed, mass of vehicle, slope of the road.
Explain how car sefety features protect the occupants of a vehicle in the event of a collision.
Air bags and seat belts
Both of these measures work in a similar way.
F=m(v-u)/t because t is in the denominator that means that if you are slowed downn more gradually (larger time for decelleration) then the force is less.
Air bage and seat belts both deform (stretch or squash) which increases the contact time and decreases the force you feel.
Side impact protection and driver cages
These are made of strong materials which spead the force of a collision over a large area, this reduces the pressure and is particularly important in side-on collisions where airbags and seat belts are less effective.
Why is it important when working with radioactivity to take measurements over long periods of time, and to repeat these readings.
This is important because of the random nature of radioactivity. Because each atom has a certain probability to decay you have to take the law of large numbers into consideration.
Define half-life of a material.
The half life of a material is the time it takes for half the atoms in a radioactive sample to decay, or the time it takes for the activity of a sample to halve.
Define and name the unit of activity
The unit of activity is the Becquerel - this is equal to one decay per second.
Explain why gamma sources with short half-lives are good for radiactive tracers.
Gamma sources are used because the penetrating power of gamma means that the radiation can pass out of the body and be detected - this fact, combined with its low ionisation means it causes the least harm. A low half-life is used so that the source becomes harmless very quickly.
Explain why gamma sources with long half lives are used in external radiotherapy.
Gamma is used because it can ionise cells from outside the body as it is highly penetrating. A long half-life is used so that the source does not have to be replaced very often.
Explain why alpha emitters with long half lives are used within smoke alarms
Alpha emitters are generally quite safe as the radiation cannot pass through the plastic casing of the device. Alpha is very ionising so this means that it is effective at ionising the air. A long half life is used as this ensures reliability as the source would not have to be replaced very often.
Describe the nature of alpha beta and gamma radiation.
Alpha radiation is a helium nucleus (2 protons and 2 neutrons joined together)
Beta radiation is a fast moving electron.
Gamma radiation is an electromagnetic wave
(you need to know the symbols for these too - find them in the revision guide)
Explain why some elements (or isotopes of elements) are radioactive.
For each proton number there is a certain range of neutron numbers that would be required to make the element stable.
If an element has too many neutrons, or not enough, they become unstable and will eventually decay.
Explain the terms proton number, nucleon number, and isotope.
The proton number of an element is the number of neutrons contained in the nucleus.
The nucleon number is the number of nucleons (protons and neutrons are both nucleons) in the nucleus of an atom.
An isotope is an element with a different number of neutrons but the same number of protons.
Explain how a stable nuclear reaction is produced in a nuclear reactor. In your answer include an explanation of the terms control rods, moderator, fuel rods, and chain reaction.
Uranium - 235 can be induced to fission by the absorption of a slow moving neutron. After uranium decays it emits 2 or more fast moving neutrons. In order to maintain a stable chain reaction - one where the neutrons from one decay are used to cause others - the neutrons need to be slowed down, and this is achieved through the use of a moderator. In order to prevent the chain reaction becoming uncontrolled, control rods are used to absorb excess neutrons.
Describe the nature of the product of nuclear fission.
The products of nuclear fission are energy, two or more neutrons, and two or more daughter nucleii (usually 2)
Daughter nucleii are radioactive and can have a wide range of half-lives.
Explain the term nuclear fusion.
Under intense heat and pressure, light nucleii - such as hydrogen, helium, and their isotopes (dueterium, tritium etc) can combine to form heavier elements.
Describe the problems with containment in fission and fusion reactors.
Fission
Pressure - high pressures need to be contained.
Neutron shielding - the fast moving neutrons produced in the decays can be dangerous to humans an need to be contained.
Fission products - The daughter nucleii produced have to be contained within the reaction vessel.
Fusion
It is difficult to contain the reaction as it needs to occur at a temperature and pressure so high that no material can withstand it - magnetic fields are therefore used.
The gamma rays produced in the fusion reaction need to be contained.
