required practicals Flashcards
specific heat capacity:
- heater and thermometer in aluminium block (add couple of drops of water, so they don’t get stuck).
- attach the immersion heater to a joulemeter to see how much energy is being passed into the heater.
- read temperature before start, and start stop clock as soon as power supply is switched on.
- turn heater on, leave it for roughly 30 minutes.
- read final temperature of the metal.
what are risks and safety precautions for the specific heat capacity experiment?
- the immersion heater/metal can become hot, resulting in burns. allow it time to cool before packing away the equipment, and do not touch it when it’s switched on.
thermal insulation:
- 80cm^3 of boiling water into a beaker, cover the top with cardboard, apart from a hole for a thermometer.
- record starting temp. of the water, and start a stopwatch.
- record the temperature of the water every 3 minutes for 15 minutes.
- repeat this process with a range of different insulating materials.
what are risks and safety precautions for the thermal insulation experiment?
- keep water away from all electrical equipment.
- do not touch hot water directly, as it can result in burns. instead, place the small beaker (containing hot water) inside a larger beaker to handle it.
resistance depending on the length of a wire:
- set up a circuit with a battery, an ammeter in series, a length of wire with a voltmeter in parallel to it, and a closed switch.
- record the length of the wire, turn on the power supply, and record the voltmeter and ammeter readings.
- turn off the power supply, change the length of the wire by a fixed amount, and repeat the process.
- calculate and record the resistance for each length of wire using the equation (r = v/I).
what are risks and safety precautions for the length of a wire experiment?
especially with shorter wire lengths, it can heat up enormously, resulting in burns if touched. allow the wire to cool before packing away, only connect the power when taking measurements to avoid overheating.
density:
regular object:
- measure the mass using a balance.
- use a ruler to measure the length of each side (length x width x height = volume).
- now multiply this volume by the mass of the object, and that’s the density.
irregular object:
- find the mass of the object using a baance.
- fill a eureka can with water, till it reaches just under the spout.
- place the object in the water. this will displace water, and we can measure how much water is displaced with a measuring cylinder.
- this volume is the same as the volume of the object
- now multiply this volume by the mass of the object, and that’s the density.
what are risks and safety precautions for the density experiment?
water spilled from the displacement can can fall on the floor and create a slip hazard. use a measuring cylinder to catch any water and prevent spills.
I-V characteristics of circuit elements:
- battery, connected by wires to a resistor. the resistor is in series with an ammeter and a variable resistor. we have a voltmeter in parallel across the resistor.
- use the voltmeter to measure the initial potential difference across the resistor.
- then use the ammeter to measure the current through the resistor.
- record these values in a table.
- adjust the variable resistor, and read the values on the voltmeter and ammeter. do this until you have a range of readings.
- switch the direction of the battery, meaning the direction of the potential difference has reversed. both the voltmeter and ammeter should have negative values.
- continue taking several readings of the potential difference and the current.
- repeat the entire experiment twice more. for the first repeat, replace the resistor with a filament lamp.
- for the second repeat, replace the filament lamp with a diode, and place a resistor in series too, as diodes are easily damaged by high current. this extra resistor will keep the current relatively low and protect the diode.
> this means the ammeter will have to
be extra sensitive, so scientists use a
‘milliammeter’.
what are risks and safety precautions for the I-V characteristics experiment?
- wires and components may become hot after a current has passed through. allow to cool before handling.
- disconnect the power supply when not taking readings to prevent overheating.
how would you set up the stretching a spring required practical?
- clamp stand, 2 bosses attaching 2 clamps to the stand
- place a heavy weight on the clamp stand to stop it from falling over
- attach a metre ruler vertically to one clamp, and a spring to the other. the top of the spring must be at the 0 point on the metre ruler
how would you carry out the stretching a spring required practical?
- read the original length of the spring against the metre ruler (unstretched length)
- hang a 1N weight on the spring, and read the new length of the spring on the ruler
- continue adding 1N weights, and reading the length of the spring
- work out the extension produced by adding each weight. subtract the unstretched length from each new reading
- plot the extension against the weight on a graph
what graph is created when extension is plotted against weight?
- straight line through the origin. directly proportional relationship
- linear relationship between force and extension, due to the straight line graph (e.g. compared to a rubber band, which creates a curvy line on the graph)
- the spring is elastic - if we remove the weight, the extension returns to 0
what is inelastic deformation?
- adding too much weight means we overstretch the spring (if we took all the weight away, it would still show an extension), and the graph becomes non-linear
- we have reached the limit of proportionality
how do you find the spring constant on a graph with force plotted against extension?
it can be found at any point by dividing the force (weight) by the extension
- it will be the same for any part of the graph, as long as we don’t exceed the limit of proportionality
what are some control variables for the Hooke’s law required practical?
room temp, diameter of spring, starting length of spring, spring material
what equipment is used for the acceleration required practical?
- toy car attached to a piece of string
- the string is looped around the pulley, and the end is attached to a 100g mass (this will provide the force acting on the toy car)
- set up a timer
- draw chalk lines on the desk at equal intervals e.g. every 10cm
what is the method for the acceleration required practical?
investigating the effect of a force on the acceleration of an object, whilst keeping its mass constant
- hold the toy car at the starting point, and let go of it when ready
- as there is a resultant force acting through the string, the car will accelerate along the bench
- record the time the car passes each distance marker, and it’s difficult to record an accurate time when the car is moving quickly
- record the experiment on a phone, then play the video back and record the times accurately - repeat the experiments several times, but decrease the mass on the string each time, meaning the force is decreasing each time
- ensure that when taking the mass off the end of the string, place it on top of the car, as this keeps the overall mass of the object the same (the object includes the car, the string, the mass, as they’re all connected)
what results should we find from the acceleration required practical?
investigating the effect of a force on the acceleration of an object, whilst keeping its mass constant
- Newton’s second law of motion states that the acceleration of an object is proportional to the force applied
- the force is the mass of the weight on the end of the string
- we should find that the acceleration of the toy car is proportional to the mass on the end of the string
how can we investigate whether:
‘varying the mass of the object affects the acceleration produced by a constant force’
- use the same equipment
- keep the force constant, e.g. using 100g mass on the end of the string
- attach a mass to the toy car e.g. 200g
- record the car as it accelerates along the bench. repeat the experiment whilst increasing the mass attached to the toy car
what results should we find from the acceleration required practical?
varying the mass of the object affects the acceleration produced by a constant force
- Newton’s second law tells us that the acceleration of an object is inversely proportional to its mass
- as we increase the mass of the toy car, the acceleration should decrease
what is a ripple tank?
- shallow tray of water
- in the water is a vibrating bar
- the bar is connected to a power pack
- when the bar vibrates it creates waves along the surface of the water
- above the ripple tank is a lamp, and beneath is a sheet of white paper
- when light shines through the water, it produces an image of the waves on the paper
how do you find the wavelength and frequency of the waves using a ripple tank?
- record the waves using a phone. play back the recording at different speeds/freeze the image completely
- to measure the WAVELENGTH, place a ruler next to the paper, then freeze the image of the waves. measure the length of a total of 10 wavelengths. to find one wavelength, divide this by ten, giving a mean wavelength.
- (record in slo-mo to make it easier) to find the FREQUENCY, place a timer next to the paper, and count the number of waves passing a point in one second. this is hard, so count the number of waves passing a point in 10 seconds, and the divide by 10, to get a mean value.
how do you determine wave speed after using a ripple tank?
- use wave speed = frequency x wavelength
- select a wave, measure the time taken for it to move the length of the tank. calculate the speed by dividing the distance travelled by the time taken
- we could get slightly different results using these two methods, due to measurement errors e.g. timing
how do you set up the practical to measure the waves in a solid?
- have a string with one end attached to a vibration generator
- at the other end of the string, we have a hanging mass, keeping the string taut
- the vibration generator is attached to a signal generator, allowing us to change the frequency of the vibrations
describe the method for measuring waves in a solid practical:
- turning on the power means the string vibrates, however, it’s difficult to see these vibrations
- at a certain frequency, we get a standing wave which is visible, due to an effect called resonance
- measure the wavelength of the standing wave, using a ruler. measure its total length
- we know the frequency, as it will be indicated on the signal generator
how do you calculate the wave speed when measuring waves in a solid?
wave speed = frequency x wavelength
- read the frequency from the signal generator
what happens to a standing wave if we increase the frequency?
we get more loops, and it’s possible to get 1 and a half loops
- to calculate a single wavelength, divide the total length by the number of half wavelengths (how many loops), then multiply by two
what does the wave speed actually depend on?
- doesn’t depend on frequency or wavelength
- depends on the tautness of the string, and the mass per cm
how do you set up the reflection and refraction required practical?
- ray box, lens, slit, producing a narrow ray of light (ray boxes get hot, switch them off when they’re not being used). could also use a laser, but that’s more dangerous
- take a piece of A3 paper, draw a straight line down the centre using a ruler. use a protractor to draw a perpendicular line, which is the normal. place a glass block against the first line, so the normal is around the middle of the block. draw around the glass block
how do you carry out the reflection and refraction required practical?
- use the ray box to direct a ray of light so it hits the block at the normal, which is the incident ray. the angle between the incident ray and the normal is the angle of incidence
- we’ll be able to see a ray reflect from the surface of the block, and see another ray leaving the block from the opposite side, which is the transmitted ray
- mark the paths of these rays with crosses, then switch off the ray box, and remove the glass block
- draw in all the rays, and draw a line to show the path of the transmitted ray through the block
- use a protractor to measure the angle of incidence, reflection, and refraction (between normal and path of transmitted ray)
- repeat the experiment again using a block of a different material (e.g. plastic such as perspex)
what should we see when we use a perspex block instead of a glass block in the reflection and refraction RP?
- angles of incidence and reflection are the same for both glass and perspex, as they don’t depend on the material
- the angle of refraction will be different, as that does depend on the material
describe a leslie’s cube:
- use a leslie’s cube to see how much infrared is emitted from different surfaces
- it has 4 different surfaces (shiny metallic, white, shiny black, matte black)
describe the method for the infrared required practical:
- fill the leslie’s cube with hot water
- point an infrared detector at each of the 4 surfaces and record the amount of infrared emitted (always keep the same distance between the leslie’s cube and the detector)
what would be the results from the infrared RP?
matte black releases the most, followed by shiny black, then white, then shiny metallic
what can we use in the infrared RP if we don’t have an infrared detector?
- thermometer with the bulb painted black
- however the resolution of the thermometer is less than the infrared detector, so we may not be able to detect a large difference between the surfaces with this
how do you measure the absorbance of infrared by different surfaces?
- infrared heater, and on either side are metal plates
- one plate painted with shiny, metallic paint and the other is painted with matte black paint
- on the other side of each plate, use vaseline to attach a drawing pin
- switch on the heater, start timing
- the temperature of the metal plates increase as they absorb infrared, and record the time it takes for the vaseline to melt and the drawing pins to fall off
- the drawing pins will fall off the matte black plate first, as it absorbs more infrared
