Heat and Temperature (And 6th year Magnetism): Flashcards
temperature
the measure of the hotness or coldness of a body
SI unit for temperature
the kelvin K
for practical work
ºC
ºC =
K - 273.15
Δθ = 5ºC =
5K
thermometric property
the physical property of a thermometer that changes measurable with temperature
4 thermometric properties
length of a column of mercury
emf of a thermocouple
resistance of a wire
colour of liquid crystals
what is the standard thermometer
the laboratory mercury thermometer
to calibrate a liquid in glass thermometer experiment
calibration graph, y axis
length cm
to calibrate a thermometer experiment
calibration graph, x axis
temperature ºC
to calibrate a liquid in glass thermometer
2 points on accuracy
- use a stirrer to ensure water has uniform temperature
2. avoid error of parallax when using the half metre stick to measure the length of the liquid in a glass tube
calibrating a thermocouple thermometer y-axis
emf (mV)
what do you place in the substance you want to check temperature of with thermocouple thermometer
hot junction
reference junction
cold junction
how to find temperature of reference junction
finding the value of the point of intersection of the graph and the x-axis
2 different thermometers
don’t agree
the values of different thermometers
will most likely not be the same
why do the 2 values not agree?
different thermometers based on different thermometric properties respond in a different way to a given rise in temperature giving somewhat different values
is there a correct thermometer?
we choose a standard thermometer against which all other thermometers can be compared
what is special about a clinical thermometer?
there is a constriction
what is the constriction in the medical thermometer designed to do?
designed to stop the liquid from falling back into the reservoir when the thermometer is taken out of the patient’s mouth
how is the liquid in the medical thermometer got back into the reservoir
it is shaken before used on next patient
2 uses of a thermocouple thermometer
in an oven or a boiler
how is the thermocouple thermometer read?
the emf generated would be translated to a temperature reading
what flows between hotter and cooler substance?
heat energy
atoms in hot and cold substances moving in
moving in a 3 dimensional type of vibration
atoms in hot and cold substances have what energy
kinetic and potential energy
energy inside hot and cold substances
internal energy
which substance has more internal energy
the hotter substance
why does the hotter substance have more internal energy?
the kinetic energy is greater due to vibrations in the hotter substance
what is heat?
the form of energy transferred from the hotter substance to the cooler substance as a result of the temperature difference between them
definition of heat capacity
the heat energy needed to change the temperature of an object by 1K
symbol of heat capacity
C
unit of heat capacity
JK -1
definition of specific heat capacity
the heat energy needed to change the temperature of 1 Kg of the object by 1 K
symbol of specific heat capacity
c
unit of specific heat capacity
J Kg -1 K-1
energy needed to change temperature formula
mcΔθ
m
mass of substance
c
specific heat capacity
Δθ
temperature change
energy needed to change temperature =
kinetic energy (1/2 m v squared )
to measure specific heat capacity by an electrical method. what do you do before the experiment?
let the arrangement stand for several minutes before the electricity is switched on
to measure specific heat capacity by an electrical method. why do you let it stand for a few minutes
to ensure that t he temperature of the liquid equals the temperature of the calorimeter
to measure specific heat capacity by an electrical method. 4 steps in the experiment
- record the mass of the calorimeter and mass of the liquid
- record the initial temperature of the liquid and calorimeter
- allow current to flow for 5 minutes, record electrical energy supplied by using the joulemeter
- record the final temperature of the liquid and calorimeter
to measure specific heat capacity by an electrical method. electrical energy supplied =
heat energy gain + heat energy gain of calorimeter
to measure specific heat capacity by an electrical method. 2 points on accuracy
- avoid small rise in temperature as measuring small values results in greater percentage errors
- use a sensitive thermometer to get a precise value of the temperature rise
what do storage heaters contain?
concrete blocks with a large value of specific heat capacity
when do storage heaters heat up and why?
heat up at night when the demand for electricity is less and is cheaper
why do storage heaters absorb large amounts of heat?
because of the large heat capacity
what do storage heaters do during the day?
they cool down by releasing their heat to the surrounding air
water can
absorb large amounts of heat
very useful liquid in radiators
water
to measure specific heat capacity by a mechanical method what do you do before the experiment
let sit for several minutes before copper is added
to measure specific heat capacity by a mechanical method what do you do before the experiment, why do you let sit for several minutes before copper is added?
ensures that the temperature of the liquid equals the temperature of the calorimeter
heat loss of hot copper =
heat energy gain of liquid + heat energy gain of calorimeter
what is the calorimeter usually made of?
copper
water at 100º and water at 20º added, heat change of hotter one
100º - x
water at 100º and water at 20º added, heat change of cooler one
x-20º
when calculating the moment of a force causing something to move in a circle, what is the perpendicular distance?
the radius
moment of a force causing something to move in a circle
IlB x radius
moment of a couple causing something to move in a circle
IlB x diameter
magnetic flux formula
Φ = BA
Φ
magnetic flux
B
magnetic flux density
A
area through which magnetic flux density is acting
unit of magnetic flux
tesla x m2
Faraday’s law - ENGLISH
if the magnetic flux lines passing through a circuit change, then an emf is induced
the induced emf is proportional to the rate of change of magnetic flux passing through the circuit
Faraday’s law - MATHS
emf ∝ dΦ/dt
emf = -N dΦ/dt
(N= number of turns in coil)
(ignore negative in maths equation)
Lenz’s law - ENGLISH
The induced emf makes a current flow in such a direction as to oppose the change that caused it
ac Resultant voltage =
source voltage - induced voltage
ac if the frequency of the a.c source is increased
the induced voltage is greater and the resultant voltage is smaller, bulb is less bright
ac if an iron core is inserted into a solenoid
magnetic flux is stronger, greater induced voltage, decrease in resultant voltage, less bright bulb
dc initially
current flows in the same direction, magnetic field is constant, no emf???
dc maximum brightness
takes time for maximum brightness to be reached
dc increase briefly induced emf 2
more turns of a wire of the solenoid
insert an iron core into the solenoid
dc if the switch is opened
self induction happens for a brief time interval, small delay in the bulb’s brightness reducing to zero
