Forces and motion
What is the equation for momentum?
p=mv
What is meant by a renewable energy source?
Sources that replenish themselves naturally and will not run out
d=m/v
What is a magnetic field?
A region surrounding a magnet where other magnets will experience a force.
Give the charges of protons, neutrons and electrons
protons - 1+
neutrons - 0
electrons 1-
What is Hooke's law
The extension of a spring is directly proportional to the force applied, until the limit of proportionality.
What are three renewable energy resources?
any three of:
Nuclear power, Solar power, Geothermal energy, Hydroelectricity, Tidal energy
How does changing the temperature of a gas affect the velocity of the particles?
Explain what a hard magnetic material is.
Hard magnetic materials get magnetised when an external magnetic field is applied and stay magnetised permanently when the external field is removed
Why is an atom neutral?
- It contains the same number of protons as electrons
- The charge of a proton is 1+ and an electron is 1-
- These charges balance, so the atom has no overall charge
What is meant by the conservation of momentum? Give the formula
Total momentum before the collision is equal to the total momentum after the collision.
m1x u1 + m2x u2 = m1x v1 + m2x v2
Describe the energy changes in a power station. (3)
- Heat energy released in the reaction is used to make steam
- Converted to kinetic energy as the steam moves the turbine
- Kinetic energy from the spinning turbine causes the generator generates electricity
What is the difference between the structure of particles in a gas and the structure of particles in a solid?
- Particles in a solid are tightly packed together (due to strong forces), arranged in a uniform structure and they vibrate in place.
- Particles in a gas are free to move (due to almost no forces), they are separated over large distances and they move at high speeds
How is electromagnetic induction used in alternators to generate alternating current?
A coil of wire rotates in a magnetic field. The end of this coil is connected to slip rings which will cause the current to change direction while rotating. This means and alternating current is produced.
Why do alpha particles have a high ionising power? (3)
- Alpha particles have a relatively large mass (as they are made up of 2 protons and 2 neutrons)
- They have a high ionising power because they interact with atoms along their paths
- This causes ions to form
Explain how a falling object reaches terminal velocity? (4)
- object accelerates as it falls due to weight
- as it accelerates, air resistance increases
- therefore resultant force decreases
- air resistance = weight so resultant force = 0 meaning acceleration = 0 - reaching terminal velocity
How does static electricity help when painting an awkward object connected to an electrical supply? (5)
- As drops emerge from the spray gun they are given a charge
- The drops carry the same charge which causes them to repel each other
- This forms a thin spray as they spread
- the object is given the opposite charge as the paint
- The paint drops are attracted to the frame allowing it to cover hard to reach areas
How would you measure the velocity of the sound in air?
Make a sound and record how long it takes to hear it over a large distance (ie larger that 50m). Use an electronic timer or timing device to record the time. Use the equation speed = distance/time to find the speed
Echo clap method - clap a long distance from a wall, record the time taken to hear the echo. Record the distance travelled, which is twice the distance between the wall and the person. Use speed = distance/time to work out the speed
How do microphones convert sound into electrical signals? (4)
- When sound is produced, the pressure variation in the waves cause the diaphragm to vibrate
- A coil of wire is connected to the diaphragm, so as the diaphragm moves the coil of the wire moves
- The coil of wire is in a magnet so when it moves a voltage is induced in the coil
- As there is a complete circuit is also created
State the sequence of the life of a star
Cloud of particles pulled together by gravity
Very high temperatures and nuclear reactions begin
stable period, balance of forces
Star expands, cools and becomes a red giant
Star collapses, increases in temperature and becomes a white dwarf
Star cools and becomes a black dwarf
Explain how safety features such as seatbelts, crumple zones and airbags reduce risk of injury in accident.
All of these safety features increase the stopping time during a collision by applying a force for longer period of time.
Since change in momentum = force x time, as stopping time increases, force applied on the driver decreases therefore risk of injury decreases.
How can static electricity cause a danger to aircrafts and how can it be avoided? (3)
- as a aircraft flies through the air, friction causes it to become charged with static electricity
- after it lands, during refueling, a spark could react with the fuel causing an explosion
- solution: after landing, earth the plane and fuel tankers with a conductor before refueling
How does sonar work?
When ultrasound waves are emitted they reflect off boundaries and their echoes are detected. The speed of the ultrasound is known and also the time it takes to detect the echoes. The equation distance = speed x time is used to find the distance between the ultrasound emitter and the boundary (the distance calculated would be double the actual distance as the sound has travelled there and back).
How does a step up transformer work? (5)
- The primary coil has fewer turns than the secondary
- An alternatign current is connected to the primary coil
- This produces a magnetic field
- The sort iron core causes that magnetic field to pass through the secondary coil
- The magnetic field induces and current in the secondary coil, but as it has more turns in the coil, the voltage will be higher.
What occurs in the stage when a star is a main sequence star?
- The fusion in the star releases energy
- During fusion, main sequence stars mostly turn hydrogen into helium
- Thermal energy released from fusion causes an outward pressure which balances the inward pressure caused by gravity
- The star is in equilibrium so will not collapse due to gravity or expand due to fusion. It is stable.