PHY 1 : PHYSICAL QUANTITIES , UNITS AND MEASUREMENTS

What is the digital micrometer screw gauge used for ?

To measure objects that are too small to be measured using digital calipers. The object is placed between the anvil and spindle of the digital micrometer screw gauge. The ratchet is turned until the spindle is in contact with the object. We need to ensure that the object is held tightly between the anvil and spindle. Do not tighten the ratchet too much.

What is precision ?

The smallest unit an instrument can measure.

What is the measuring range , smallest division and example of usage for the measuring tape ?

MR : zero to several metres , SD : 0.1cm or 1mm , a person’s waist

What is the measuring range , smallest division and example of usage of the metre rule ?

MR : zero to one metre , SD : 0.1cm or 1mm , height of a table

What is the measuring range , smallest division and example of usage for digital calipers ?

MR : zero to 15 centimetres , SD : 0.001cm or 0.01mm , diameter of a test tube

What is the measuring range , smallest division and example of usage for digital micrometer screw gauge ?

MR : zero to 2.5 centimetres , SD : 0.0001cm or 0.001mm , diameter of a wire

When recording the measurements, we can record the measurements shown on the digital display of the digital calipers to

0.1 cm

When recording the measurements, we can record the measurements shown on the digital display of the digital micrometer screw gauge to

0.01mm

What is parallax error ?

When our eyes are not perpendicular when measuring .

How can you minimise errors when measuring lengths ?

You could measure from another point and substract it from the final reading or take several readings and calculate the average.

What is one oscillation ?

Each complete to-and-fro motion

What is the period of a simple pendulum ?

Time taken for one complete oscillation

What affects the period of the pendulum ?

Its length

How can pendulum clocks measure time more accurately ?

Pendulum clocks can be calibrated by adjusting the length of the pendulum.

What other periodic motions can be used to keep time ?

The oscillations of springs and natural vibrations of crystals.

Why are quartz crystals used to keep time ?

They are small , accurate and require very little electrical power.

What is the average reaction time for most people ?

0.3-0.5s

Why do we usually take time readings to one decimal place ?

Since stopwatches need to be started and stopped by hand , this manual operation introduces a random error called human reactions time.

What are scalar quantities ?

They are physical quantities who have only magnitude.

What are vector quantities ?

They are physical quantities that have both magnitude and direction .

State examples of scalar quantities .

Distance , speed , mass , energy , time , pressure , work done .

State some examples of vector quantities.

Displacement , velocity , acceleration , force , weight , moment / torque.

What is distance ?

The total length covered by a moving object regardless of the direction of motion. A scalar quantity ( has magnitude only ) . SI unit : metre ( m )

What is displacement ?

The distance measured in a straight line in a specified direction. A vector quantity ( has both magnitude and direction ) . SI unit : metre ( m )

What is speed ?

Speed is the distance moved per unit time . It is a scalar quantity , SI unit : metre per second ( m/s)

What is velocity ?

It is the rate of change of displacement. It is a vector quantity. Its SI unit : metre per second ( m/s ).

What is a physical quantity ?

A physical quantity is a quantity that can be measured , which consists of a numerical magnitude and a unit.

What are the 7 base quantities ?

Length, mass , time , electric current , thermodynamic temperature , amount of substance and luminous integrity.

What is the SI unit and symbol for length ?

SI unit - metre , symbol ( m )

What is the SI unit and symbol for mass ?

SI unit - kilogram , symbol - kg

What is the SI unit and symbol for time ?

SI unit - second , symbol ( s )

What is the SI unit and symbol for electric current ?

SI unit - ampere , symbol - A

What is the SI unit and symbol for thermodynamic temperature ?

SI unit - kelvin , symbol - K

What is the SI unit and symbol for amount of substance ?

SI unit - mole , symbol - mol

What is the SI unit and symbol for luminous intensity ?

SI unit - Candela , symbol - cd

What is a derived quantity ?

They are physical quantities that are derived from the basic quantities / physical quantities not part of the 7 basic quantities Example : speed is defined as distance travelled per unit time. basic quantity : length , time derived quantity : speed

How to remove a prefix ?

multiply it by its factor

How to add a prefix ?

divide it by its factor

What are prefixes ?

definition : letters placed in front of words to make new words help represent very small or very big physical quantities

What are the ' multiple ' prefix ?

tera- ,giga-, mega- , kilo-

What are the sub-multiple prefix ?

deci - , centi-,milli-, micro - , nano -, pico -

What is the category , factor and symbol for the prefix ' tera - ' ?

multiple , factor is 10 12 , symbol : T

What is the category , factor and symbol for the prefix ' giga- ' ?

multiple , factor : 10 9 , symbol : G

What is the category , factor and symbol for the prefix ' mega- '?

multiple , factor : 10 6 , symbol : M

What is the category , symbol and factor for the prefix ' kilo-' ?

multiple , factor : 10 3 , symbol : k

What is the category , symbol and factor for the prefix ' deci- ' ?

sub-multiple , factor : 10 -1 , symbol : d

What is the category , factor and symbol for the prefix ' centi- ' ?

sub-multiple , 10 -2 , c

What is the category , symbol and factor for the prefix ' milli- ' ?

sub-multiple , 10 -3 , m

What is the category , symbol and factor for the prefix ' micro - ' ?

sub-multiple , 10 -6 , ( weird long u )

What is the category , factor and symbol for the prefix ' nano - ' ?

sub-multiple , 10 -9 , n

What is the category , factor and symbol for the prefix ' pico - ' ?

sub-multiple , 10 -12 , p

What is standard form ?

A way of writing numbers , in which a number between 1 to 10 is multiplied by an appropriate power of 10 - convenient and acceptable way of expressing physical quantities examples : 0.00567 = 5.67 x 10 -3

What is the SI unit for length ?

metre ( m ).

What are the metre rule and measuring tape have in common ?

Instruments commonly used to measure length .

Use of metre rule .

measure lengths up to one metre

Use of steel measuring tape

measuring straight distances longer than a metre

Use of cloth measuring tape.

measuring length along curved surface : diameter of tree trunk / waist

Use of digital calipers.

measure external and internal diameters of an object accurately. the object is gripped gently using the jaws of the digital calipers and the circumference of the object is shown on the digital display .