Explain why the minimum force needed to close the computer is likely to be less than 4.2N. (2)
- The lid is pulled down by its weight and the force of gravity. - Acts in same direction as closing force, anticlockwise.
How to find the distance of an object in a mirror?
Look down sighting pins line is drawn through the mirror . A line is also drawn from the object directly to the mirror. The lines should cross behind the mirror, here is the position of the object.
When finding the distance of an object in a mirror, describe how the student can be able to confirm that the position of the image is correct. (2)
- Measure distances to mirror - Object distance = image distance.
Statements that are correct about a mirror? (2)
- The image in a plane mirror is virtual - The angle of incidence equals the angle of reflection.
If 200J of energy is put in and 1800J is useful and 200J is lost to surroundings how efficient is the devise?
Why does a heating element is a kettle get hot when its electrical supply is switched on? (2)
- Energy from the supply of electrical energy is transferred to thermal energy. - The transfer to thermal energy vibrates the particles in the water. The current is causing a heating effect in the element as there is a resistance.
Why have a fuse at a specific value just over the normal? (2)
Only one above working current. When the current goes over the specified value there is no delay, the fuse will just blow.
2 mA in A?
Ways to check experiment data is accurate with measuring cylinder and balance?(2)
- Check balance is zero. - Measure from bottom of meniscus.
Coffee cups exam question (4) - Cups are same size one has more coffee in, compare pressures in the coffee at the bottom of each cup?
- Pressure greater in the full cup, less in the half full cup. - reference to pressure equation p = W / A - depth/mass/weight of liquid different in each cup. - density of liquid is the same in each cup.
The energy from the beta radiation is expected to destroy the cells in the tumor over a period of weeks, what would be the most suitable half-life of the isotope. 75 mins, 75 hours, 75 days, 75 years. EXPLAIN CHOICE!
75 days. - The isotope will last for long enough. - A and B may need to be replaced.
A straight line graph is a......
A curved line graph is a....
Describing an experiment....
Equation measuring detail of measurement e.g 50m repeat/averaged how to make measurement
- In the dark and at low light levels, the resistance of an LDR is high, and little current can flow through it. - In bright light, the resistance of an LDR is low, and more current can flow through it. NON-LINEAR
- At low temperatures, the resistance of a thermistor is high, and little current can flow through them. - At high temperatures, the resistance of a thermistor is low, and more current can flow through them.
Explain why a voltage is induced?
Wire cuts magnetic field lines.
One way to increase voltage?
When question mentions energy transfer....
Mention efficiency equation. efficiency = useful energy output / total energy input
1 watt is the same as......
1 Joules / per second
How many W in Kw
Newtons 1st Law
The First Law states that objects with balanced forces acting on them will stay at rest, or in constant motion.
Newtons 2nd law
The extension of an elastic object is directly proportional to the force applied to it: F=KE
reason for acceleration change in car?
Increased Friction Increased Air resistance GRAPH IS NON-LINEAR
electronic balance measures......
when does a uniform magnetic field occur?
Two opposite poles brought close together. Magnetic field lines and parallel and move from north to south
Explain how to produce a uniform magnetic field?
- Two permanent bar magnets. - Poles arranged correctly, North facing south - Idea of magnets being the correct distance apart
Method to measure background radiation?
Remove source measure background count repeat and find mean subtract from experimental values
Explain why ........ is a suitable tracer?
Half life is long enough..... activity would quickly reduce when not needed anymore..... gamma radiation can be detected out of the body.
Describe how sound waves move through the air?
occelation of the air molecules longitudinal waves direction of vibration is parallel creates a pressure wave that is then picked up.
Water is being heated by heater coil, water reaches a steady value below the boiling point of water, explain why?
idea of energy losses. rate of energy loss = rate of energy supply
idea of energy losses?
rate of energy loss = rate of energy supply
Explain why comets travel faster when getting closer to earth? Use ideas of energy?
Grav pot reduces when closer, KE increases. because total energy is conserved
differences between X-rays and visible light?
X-rays have shorter wavelength X-rays have higher freq
Explain why the acceleration is not constant, even though the engines produce a constant force?
Air resistance increases as velocity increases reducing resultant force
How are microwaves used for heating?
electromagnetic waves penetrate in the food particles vibrate with greater amplitude conduction through the rest of the food
How is food heated in pan?
conduction from hot plate to pan conduction through pan conduction from pan to water convection in water conduction from water to food
Two conditions required for total internal refection?
angle of incidence has to exceed the critical angle. Material must be optically dense.
Advantage of optical fibers?
Sends more information per second
What is an independent variable?
In an experiment, the independent variable is the variable that is varied or manipulated by the researcher,
What is the dependent variable?
the dependent variable is the response that is measured.
Example of direct proportion graphs?
This is straight and linear.
What is Density?
Density compares masses to volumes. So as the mass increases the volume will increase.
The purpose of a moderator in a nuclear reactor?
Slows down neutrons.
Describe how a loudspeaker uses an electrical supply to produce sound waves?
Current is created in the coil Alternating current used a magnetic field is created Flemmings left hand law force on the coil vibration in coil makes longitudinal wave
Why might the claimed efficiency for a heater, not be accurate?
Does not allow for energy loss.
Why is there a delay when heater is starting up?
Time for heat energy to transfer through the coil and to the measuring device?
Why is there a delay when heater is starting up?
Time for heat energy to transfer through the coil by the coil and to the measuring device?
Rise in temperature as a hater is switched on?
Heat transfers through block by conduction, greater then output energy.
Heater no longer increases temperature of object?
- Energy lost to surroundings - most of the heat supplied is lost, energy input and output nearly equal.
How is kinetic energy energy gained related to the work done?
They are equal.
One watt of power is the same as?
1 joule per second.
Order of planets?
My Very easy method
Explain why forces on a object must be balanced?
- acceleration requires unbalanced force. - constant velocity means object is not accelerating.
Explain why as the light enters the glass block it is refracted towards the normal?
Wave is changing in speed. The glass is more optically dense and has a higher RI then that of air.
Equation linking refractive index and critical angle?
sinC = 1/n
Suggest why Uranium 238 is the most common isotope of uranium?
Other isotopes have decayed more quickly.
What is the purpose of a moderator in a nuclear reactor?
It is able to slow down the movement of neutrons.
Uses for ultrasound range finding cars?
-Back of car emits ultrasonic pulse -Sensor on car times how long until echo returns -Knowing the speed of sound, electronics used to calculate distance with equation s=d/t
What is a virtual image?
Formed when the light rays bouncing off an object onto a mirror are diverging, so the light from the object appears to be coming from a completely different place.
Diagram of Virtual image
Three uses of Radioation
-Gamma used for industrial tracers
- Radioactive Dating of Rocks and Archaelogical Specimens.
- Nuclear powerstations.
ways to protect from radiation?
full radioactive suits to stop particles getting on skin or being breathed in.
remote control robot.
Radioactive waste, powerstations?
Radioactive low levels, disposed by burying
High level radioactive waste?
This can stay radioactive for thousands of years, stored in glass blocks that are incased in metal and then stored underground.
consequences to metal being bureied?
Earthquakes can damage the caseing. This can cause radioactive substances to be relased into groundwater which can damage plants and drinking water supplys.
Newtons third law of motion
For every action there is an equal and opposite reaction.
Residuel Current Circuit Breaker
Detects difference in current if someone touches the wire and quickly cuts the power by opening the switch.
operate much faster then fuses. No need to melt.
The RCCB will pick up Small current changes that may not melt a fuse.
They are more protctive.
advantages of circuit breakers
when a surge is detected they will open
Can easily be reset and does not need replecing.
Colors of rainbow
richard of york gave battle in vein