Diffraction and Interference

Introduction to PhysicsMeasurement,Significant Digits,Precision & AccuracyKinematicsPosition and MotionMotion involves a change in the position of an object over time.Motion can be described using mathematical relationships.Many technologies that apply concepts related to kinematics have societal and environmental implications.Big Ideas in KinematicsDynamicsForces and the Causes of MotionForces can change the motion of an object.Newtons Three Laws of Motion that govern how forces change motionApplications of Newtons laws of motion have led to technological developments that affect society and the environment.Big Ideas in DynamicsEnergyAbility to Do WorkEnergy can be transformed from one type to another. Energy transformations are never 100% efficient.Applications that involve energy transformations (e.g. power generation) can affect society and the environment in positive ways, but also have negative effects.Big Ideas in EnergyElectricity and MagnetismWaves & SoundBehaviour of Waves and Properties of SoundYou throw a coin horizontally off the CN Tower at exactly the same time that your friend drops a coin. Compare the time in the air for both coins and their paths to the ground. Group Learning: Practice Question #1You see a number of birds sitting contentedly on a horizontal electrical wire. You wonder why they do not experience an electric shock. Group Learning: Practice Question #2Explain what happens to the pitch of a siren from an ambulance or fire truck as it approaches and then passes a stationary observer.Group Learning:Practice Question #3In a collision between a mosquito and the windshield of a speeding SUV, compare the force that each exerts on the other.Group Learning:Practice Question #4Significant DigitsLimitation of MeasurementA Justification for Sig DigsMeasurements are not perfect.Measurements are not perfect.

They always include some degree of uncertainty because no measuring device is perfect. Each is limited in its precision.A Justification for Sig DigsA Justification for Sig DigsMeasurements are not perfect.

They always include some degree of uncertainty because no measuring device is perfect. Each is limited in its precision.

Note that we are not talking about human errors here.PrecisionWe indicate the precision to which we measured our quantity in how we write our measurement.PrecisionWe indicate the precision to which we measured our quantity in how we write our measurement.

For example, which measurement is more precise?15 cm15.0 cm

PrecisionWe indicate the precision to which we measured our quantity in how we write our measurement.

For example, which measurement is more precise?15 cm15.0 cm This one, obviously.

What we meanWhen we write 15 cm, we mean that weve measured the quantity to be closer to 15 cm than to 14 cm or 16 cm

BUT

When we write 15.0 cm, we mean that weve measured the quantity to be closer to 15 cm than to 14.9 cm or 15.1 cm.SignificanceDigits that have been measured are said to be significant.

15 cm This measurement has 2.15.0 cm This measurement has 3.The following rules are used to determine if a digit is significant:All non-zero digits are significante.g. 42.5 N has three significant digitsThe following rules are used to determine if a digit is significant:All non-zero digits are significantAny zeroes placed after other digits and behind a decimal are significante.g. 1.50 kg has three significant digitsThe following rules are used to determine if a digit is significant:All non-zero digits are significantAny zeroes placed after other digits and behind a decimal are significantAny zeroes placed between significant digits are significante.g. 30.07 m has four significant digitsrules to determine if a digit is significant:All non-zero digits are significantAny zeroes placed after other digits and behind a decimal are significantAny zeroes placed between significant digits are significantAll other zeroes are not significante.g. both 100 cm and 0.004 kg each have only one significant digitHow many significant digits are there in each of the following?1.10 A0.017 h102.5 MHz2100 kJ250.0 W60.80 kg0.0018010 kmThe Final AnswerWhen a measurement is used in a calculation, the final answer must take into consideration the uncertainty in the original measurements.

Note: Exact numbers used in calculations (e.g. a factor such as in the equation K=mv2) are not measurements and do not have any uncertainty.Addition and SubtractionWhen adding or subtracting measurements, the final answer should be rounded off to the least number of decimals in the original measurements.

e.g.5.124 cm (3 decimal places)+0.01 cm (2 decimal places)5.13 cm (2 decimal places)Multiplication and DivisionWhen multiplying or dividing measurements, the final answer should be rounded off to the same number of sig digs as are in the measurement with the least number of sig digs.

e.g.5.124 cm (4 sig digs)x0.01 cm (1 sig dig)0.05 cm2 (1 sig dig)