grade 8-9 theory Flashcards
Explain how the value obtained for the specific heat capacity would change if the insulation around the lead block had a higher thermal conductivity.
Energy transferred at a higher rate to surroundings.
More energy transferred for a given the increase in temperature- higher value for sph
Temperature of metal will increase at a lower rate
What is thermal conductivity?
Movement of free electrons and vibrating atoms within the material.
The higher the thermal conductivity of a material, the higher the rate of energy transfer by conduction across the material and the faster it warms up.
Evaluate the benefits and drawbacks of wind power and less coal to supply energy needs.
pro: More sustainable, Reliable, reduces harm to environment, doesn’t produce CO2 emissions, doesn’t release sulfur dioxide > acid rain > destroy habitats
Whereas coal is non renewable, Releases CO2 into atmosphere, Contributing to greenhouse effect.
con: Wind is less reliable and cannot be generated when not windy> supply issue, coal is reliable.
Wind power cannot be increased to meet demand, whereas coast stations can be made to generate greater rate.
Wind turbines are noisy and eyesore
The student wants to connect a hit in parallel with one component, so when temperature decreases, the potential difference across heater increases and get hotter. Which component?
Thermistor.
When temperature decreases, resistance of thermistor increases.
Potential difference of thermistor increases.
Connected in parallel means potential difference across heater is equal to potential difference across thermistor.
Increasing the current > increases temperature of heater.
Explain how reading on A1 compares to reading on A2 in a Parallel circuit as potential difference increased.(4)
In parallel circuit current is split between branches.
In parallel circuit potential difference is the same in each branch.
more Current flows down paths with lower resistance
Current is inversely proportional to resistance.
Current is directly proportional to potential difference.
Potential difference increases the total current in the circuit increases.
The resistance of a resistor is constant for all values of current.
But as potential difference across bulb increases, resistance increases.
so As resistance of bulb increases, it will receive a smaller fraction of the total current.
At a potential difference, when the bulb and resistor have equal resistances, the readings on A1 and A2 will be equal.
If potential difference increases, the bulb’s resistance will become greater than resistors.
So the bulb’s current will be less than the resistors current.
Explain how the total resistance of the circuit changes as the potential difference of the power supply is increased in series circuit
Total resistance of a series circuit is equal to the sum of all resistances.
As potential difference increases, current increases > resistance decreases.
So as potential difference of power supply increases, total resistance decreases.
Charge cannot flow through the car’s tires, so there is a now a large potential difference between the car and the ground suggests why it would be dangerous for a person to approach the car.
The persons is at 0 volts so there is a large potential difference between the person and the car.
Charge in the car could jump from the car to the person
Causing a current to flow through the person.
Giving them an electric shock which could injure them.
Students rubs together 2 insulating objects. When he tries to move them apart, he feels the force of attraction between them. He finds the attractive forces decrease as the objects are moved further apart. Explain why.(4)
The insulating objects have become electrically charged.
Because negatively charged electrons have been rubbed off of 1 and transferred to the other.
The insulating object that gains electrons become negatively charged.
The insulating object that loses electrons has an equal positive charge.
Since the objects are now charged, an electric field is generated around them.
The objects’ electric fields interact.
Interaction causes them to exert a non contact force on each other.
Objects have opposite charges they will attract.
Electric fields get weaker with greater distance
So there is a smaller force of attraction between them.
Both B has half the mass of bow A. Explain the difference in the temperature increase of the ball B(4)
The energy needed to change temperature and state of assistance is proportional to its mass.
ball b Has half the mass of ball a so 1/2 the energy is needed to change the temperature and states of bow B.
Energy is transferred to bow B at the same constant rate, so the amount of energy needed would be supplied in half the time.
The two are made from the same material, so the melting point is the same (so the flat section on the temperature time graph must be at the same temperature
Underwater air bubbles increase in size as they rise up. Explain why. (2)
Pressure increases as depth increases = pressure decreases as depth decreases
So the pressure outside an underwater air bubble decreases as it rises.
So the pressure outside the bubble is less than inside.
pressure Increases as volume increases
The volume inside the air bubble increases until the pressure inside the bubble is equal to the pressure outside.
p1V1=p2V2
Use knowledge of particle model to explain why the pressure inside an oxygen cylinder decreases as oxygen is removed from it.
- the Force on the walls of the cylinder is equal to the sum of all the forces exerted by all the particles in the cylinder on the cylinder walls.
- P=F/A
- a Fewer oxygen particles than the particles hit the walls less often and with smaller force so pressure will decrease.
Cylinder carried up a mountain. The temperature decreases higher up the mountain. Explain how the pressure in the cylinder changes.(4)
As altitude increases, temperature decreases.
The average amount of KE stored it’s proportional to the temperature.
KE is it’s velocity^2
So average speed of particles decreases
So hit the walls with less force and less frequently.
So force acting on the walls decreases.
P=F/A
So pressure decreases.
Periodic table doesn’t give value of mass number for each elements.
Different isotopes of same element.
Auto jobs have same atomic number but different mass number, so element doesn’t have one fixed number.
Company doesn’t declare contaminated water safe to drink until it is below 25 kilometers per minute for more than 24 hours. Why?
Activities around the process. A single reading below 25 doesn’t necessarily indicate the cut rate will stay below.
Explain how radiation source , detector and turbine blades can be used to determine a crack in the turbine blade.(3)
Gamma radiation directed through blade towards the detector.
The blade will reduce the amount of radiation reaching in the detector.
When there is a crack, less radiation will be absorbed and the count ray detected will increase so the crack can be detected.
Suitable properties of radioactive isotope for a medical tracer.
-Releases gamma radiation> high penetration to be detected outside body.
- doesn’t give off radiation > dangerous inside body
- long enough half life > still emit radiation once drunk by patient to be traced
Why does patients have to be monitored when drinking radioactive source
Gamma beta radiation can pass out of body and irritate others nearby.
Damage cells.
Evaluate risks of contamination and irradiation.(6)
Risk of contamination if uranium gets onto skin or breathed in.
Uranium emits alpha particles > inside body.
Gamma radiation isn’t as dangerous inside the body as alpha radiation.
Irradiation by uranium risk high > gamma can easily penetrate deep into body and damage organs.
Alpha cannot penetrate body, so gamma radiation more dangerous outside.
Radiation shielding material helps protect against irradiation.
Breathing masks protect against contamination.
Protective gloves protect against contamination.
Sealed zips protect against contamination irradiation.
Every star starts its life as a gas Cloud. Explain how the pressure in the gas cloud changes if the cloud is heated
Energy transferred to kinetic energy store of the particles of the gas.
Particles collide faster and more often with greater force.
Increase in pressure
service Lift has double the power of the tourist lift. The maximum mass of the service left is 4 times the maximum mass of torus lift. Explain how average speed of service lift compares 2 tourists lift at full capacity. Both have same efficiency.(4)
-P=E/t power is rate of energy transfer
- the power of the service lift is double the torus lift, so transfers twice as much energy per unit.
-GPE = 0.5mgh
- however, maximum mass of four times greater, so needs four times as much energy to raise the lift.
-t=E/P service lift t=4E/2P so 2 times longer
-so half the speed
we can assume GPE=KE when object has no initial velocity > so no energy in its KE store
and no energy lost due to friction/air resistance to surroundings
Explain why solid matter on Earth is less dense than neutron star matter.(2)
Solid matter on Earth is made of atoms closely packed together, which are mostly empty space.
Neutrons do not contain this empty space and so have more mass per volume, so greater density.
Nuclear generator vs solar cells of powering satellite.(6)
Nuclear generator: Longer lifetime and can produce power in any conditions.
Nuclear waste would have to be stored securely on board.
risk Of irradiating astronauts.
Risk of nuclear accidents releasing radiation near Earth.
Nuclear reactor needs fuel to run > has to be launched
Nuclear reactor is complex > maintenance
Nuclear reactor have to be brought down to Earth.
Solar cells: no fuel needed, no radiation safety concerns. No pollution. Nor waste. Less complex > less maintenance.
No electricity generated when in the shadow > problem in case demand / emergency
A lifetime is shorter.
Explanation Of background radiation dose(3)
Source of background radiation is cosmic rays from space which are absorbed by the atmosphere.
When in space, there are more cosmic rays since no atmosphere to absorb them.> background radiation higher.
High up in the atmosphere, there are more cosmic rays than on Earth have been absorbed by the atmosphere.
And pilots have to wear devices that measure radiation dose at work.(2)
receive higher radiation dose.
Can cause cancer.
Potassium iodide tablet absorb iodine. Explain how this minimizes damage in body (4)
Iodine is dangerous when inhaled as beta radiation is ionizing and can cause damage to body.
If iodine absorbed by thyroid, it will remain in the body for a long time.
Tablets prevent radioactive Iodine from being absorbed by thyroid.
Stable iodine does no harm and iodide 131 is removed from body.
Minimizes time that ionizing radiation spends in the body, so minimizes damage through irradiation
