required practicals Flashcards
specific heat capacity:
aim: to determine the specific heat capacity of a solid block by measuring the amount of energy required to change its temperature
- heater (attached to power supply) and thermometer in aluminium block (add couple of drops of water/vaseline, 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.
- take second temperature reading at 1 minute. take it every minute for the next 10 minutes
what should you ensure when reading thermometers?
get to eye level with the liquid line, to avoid a parallax error
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.
what is an alternative to using a joulemeter in the specific heat capacity required practical?
P=VI
- add an ammeter in series and a voltmeter in parallel
- multiply the two values (shouldn’t change) together to get the power (rate of energy transfer) to the metal block
what are the different variables for the specific heat capacity required practical?
independent: type of material
dependent: temperature rise
control variables: mass of material, surface area of material
thermal insulation:
aim: to investigate how insulation thickness affects the rate of energy transfer
- 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 (wait till thermometer liquid stops moving up), and start a stopwatch.
- let the water cool down for 5 minutes, take the end temperature
- repeat this process with a range of different insulating materials, and also repeat the different materials each time to ensure accuracy and consistency of results
what is the purpose of the cardboard lid in the thermal insulation practical?
to insulate the beaker, holds the thermometer
what are the variables for the thermal insulation practical?
independent: number of layers of insulating material
dependent: temperature change of water
control: amount of water in each beaker, starting temperature of water in each beaker
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:
aim: investigate relationship between length of wire and its resistance
- 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. they’re all connected with crocodile clips
- 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 by moving the crocodile clip along, and repeat the process.
- calculate and record the resistance for each length of wire using the equation (r = v/I).
what wire is used in the resistance of a wire practical?
nichrome wire, as copper wire has too small a resistance to measure
what are the variables for the resistance of a wire practical?
independent: length of wire
dependent: resistance of wire
control: thickness of the wire, material of the wire, temperature of the wire
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.
why can’t we let the wire get too short in the length of a wire practical?
too short a wire means the resistance is too small, and the current gets too large. the wire heats up, and this causes its resistance to change, throwing off the results
what trend can we expect to see in the graph for the resistance of a wire practical?
resistance and length of the wire are directly proportional - as one increases, the other increases
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 do you do if the solid floats in the density practical?
carefully push it under the water, but ensure your finger does not go into the water itself, as that could skew the results
how do you investigate the density of a liquid?
- place the beaker on the balance, zero the balance
- measure a volume of 50cm^3 of the liquid, and add this into the beaker, record the mass
- calculate the density by dividing the mass of the liquid by its volume (1cm^3 = 1ml)
why measure the mass of an object before placing it in the displacement can in the density practical?
when the object is placed in the water, it will get wet and influence the mass reading
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.
what are the variables for the density required practical?
independent: material being measured
dependent: density of the material
control: temperature
what are the variables for the IV-characteristics required practical?
independent: voltage across the circuit component being measured
dependent: current flowing through the circuit component being measured
control: temperature of the circuit
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. have a switch in series too
- turn on the switch, 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’.
describe the trend in the IV graph for a filament lamp:
at low voltages (both positive and negative), the current is proportional to the voltage. at higher voltages, the current plateaus due to an increase in resistance of the filament