Lecture 21

Question 1

Temperature

Answer 1

Temperature is a property of an object (is a number indicates the hotness of coldness of the object) and related to the Average K.E of atoms and molecules in that object (is a measure of K.E)

A temperature is a number related to the average kinetic energy of the molecules of a substance. If the temperature is measured in Kelvin degrees, then its value is directly proportional to the average kinetic energy of the molecules of a substance.

KE = 1/2mV^2

V increase, T increase

T =kelvin

Question 2

Heat

Answer 2

is a form internal energy and not property of an object (Total KE + potential energy of all molecules)
Arises from microscopic motion the atoms/molcules

is defined as: internal energy that flows as a result of temperature differences.

Ex: find The speed of oxygen molecules at zero oC:
Note: use Kelvin’s temp and 1atm (u) = 1.66 x10-27 Kg.
k= 1.38x10-23 J/K
use this equation.
Answer : 461 m/s

KE=1/2mV^2 = 3/2KT

is actual energy measured in Joules or other energy units

When you add heat to a substance, you are adding energy to the substance.

This added heat (energy) is usually expressed as an increase in the kinetic energies of the molecules of the substance.

If the heat (energy) is used to change the state of the substance by melting it, then the added energy is used to break the bonds betweenthe molecules rather than changing their kinetic energy.

the energy stored in chemical bonds, is considered a form of potential energy.

Question 3

internal energy

Answer 3

depends upon on temp and mass. internal energy

Same T but vastly different amounts of heat energy. Higher no. of molecules in iceberg

Question 4

When heat, (i. e., energy), goes into a substance two things can be happened:

Answer 4

1- The substance can experience a rise in temperature,
increase temp, increase volume, increase in kinetic energy

2- The substance canchange state (or phase). For example:

if the substance is ice, it can melt into water. this change does not cause a temperature rise. the energy used to break bonds.

When you add heat to a substance, you are adding energy to the substance.
This added heat (energy) is usually expressed as an increase in the kinetic energies of the molecules of the substance.
If the heat (energy) is used to change the state of the substance by melting it, then the added energy is used to break the bonds betweenthe molecules rather than changing their kinetic energy.

Question 5

Heat

Answer 5

In nature, heat always flows (transfers) from regions of high T to regions of low T

From: Hot- to – cold- until common temperature reached

Question 6

Heat transfer results in:

Answer 6

Heat gain can increase the temp.
Heat loss can decrease the temp. (taking heat away)

Question 7

Heat transfers by

Answer 7

Conduction, Convection and Radiation.

Question 8

Heat Units :

Answer 8

Heat is a form of internal Energy in a system.

Measured in calories and Joules
calorie (cal): is defined as the amount of heat necessary to raise a temperature of 1 g of water by one degree Celsius

1cal= 4.186 Joules
1kcal =4.186 x103 Joules

Question 9

Example

Answer 9

After a heavy meal one found that he overrated by 500 kcal, to get rid of the extra calories he decided to do some work ( climbing a mountain ). What is the vertical height he must walk up if his mass is 60 kg?

Work done = mgh
500 kcalx 4.286 x103 = 60 kg x9.8m/s2xh
h= 3600 m
If human body efficiency is 20% therefore
0.2 x3600=720m
He needs to climb a mountain 720m high

Question 10

Differences between Heat and Temperature

Answer 10

Question 11

Temperature Scales(Units)

Answer 11

SI scale is Kelvin (K), but more normal to use Celsius (oC) or Fahrenheit (oF) Scales

Both scales are based on the freezing and boiling points of water.

water boils at 100 degrees celsius and freezes at 0 degrees celicus

Question 12

Graph of volume vs Temp.

Answer 12

(Charles’s law) : At const. pressure, the volume of the gas increases with temp. At constant rate

-273 degrees is the absolute temp.

P=constant

the graph shows that any gas cooled to
-273 oC would have zero volume

At lower temp. negative volume has no meaning
-273 oC considered the lowest temperature possible.

This temperature is called absolute zero temperature.

Absolute zero forms the basis of the temperature scale known as the absolute or Kelvin scale.
T(K)=T(oC) +273

Question 13

Scale conversion

Answer 13

TC = TK – 273.15degrees

TF= 9/5Tc + 32degrees

Tc=5/9(Tf-32degrees)

Question 14

Thermometric properties

Answer 14

Thermometers: are instruments based on a change in some physical characteristic which can be used to measure temperature.

Examples:
Thermal Expansion
* e.m.f. of a thermocouple
* pressure of a gas at constant volume
* volume of a gas at constant pressure
* resistance
* colour
pyrometeror infrared-sensing thermometer.

PV= nRT

Question 15

Various types of thermometers

Answer 15

use thermometric properties of various substances.

Both devices depend on the expansion as the temperature increases

Liquid crystals can be constructed to change colour at a very specific temperature.

Length of a liquid column

Electric properties of the thermistor (semiconductor) can be used to measure temp.

Question 16

Infra Red Radiation Thermometer

Answer 16

Measures the temperature of the infrared heat given by the eardrum and surrounding tissues

Question 17

Gay-lussac law

Answer 17

Pressure of a gas at constant volume
Pressure increases
measurably
with temperature

PV=nRT

Question 18

Charles law

Answer 18

Volume of a gas at constant pressure

Volume increases measurably
with temperature

Dv= vob DT (b is Coeff. of Vol. Expansion)

Question 19

Thermal expansion of mercury
example:

Answer 19

What is the change in length of a column of mercury 3.0 cm long if its temperature increases from 37 oC to 40 oC. ( the coefficient of linear expansion is a= 60x10-6/oC).

DL= LaDT
= (3 cm)(60x10-6/oC)(40oC - 37oC)
DL= 5.4x10-4 cm

Question 20

Heat and Human body

Core temperature (Tc)

Answer 20

Core temperature (Tc), core body temperature, is the temperature of the internal organs, such as the liver, located deep within the body.

human body maintains its core temperature within a very narrow range of 36.5-38.5

Question 21

Peripheral Temperature Measure through:

Answer 21

Oral:3 min, 0.4oC lower than core T

Axillar:0.9oC lower than core T

The skin on the forehead(temporal):

lower by 0.3 to 0.6 oC

Question 22

rectal temperature

Answer 22

Rectal measurements closer to core temp.

Rectal 10cm from sphincter 0.3-0.8 degrees Celsius higher than core

Question 23

Physiological state

Answer 23

Daily variation in body temperature, ranging from about 37.5oC from 10 a.m. to 6 p.m., and
falling to about 36.4 oC from 2 a.m. to 6 a.m

Question 24

isotherms

Answer 24

core of deep body temperature shrinks in cold, so peripheral shell of cooler tissue left

Isotherm: distribution of temperature

Question 25

Body temperature assessments and heat content

Answer 25

mass-weighted average temperature of body tissues

H=sp x mass x temp.