Unit1: Physical Quantities & Units
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This document provides an overview of the AS Level Physics course and discusses key concepts related to physical quantities, including: 1. Physical quantities can be quantified by measurement and have units associated with them. There are two types: base quantities and derived quantities. 2. Base quantities are the seven SI base units: length, mass, time, electric current, thermodynamic temperature, amount of substance, and luminous intensity. Derived quantities are formed by mathematical relationships between base quantities. 3. When writing the units of a derived quantity, the formula is used to express the units in terms of the base units. Examples of deriving units for acceleration, force, and pressure are provided.
Unit1: Physical Quantities & Units
- 1. CI Advanced Subsidiary Level PhysicsCourse Code: 9702
- 2. Physics 9702AS & A2
- 3. The A Levels Physics course:Resource Materials:cie.org.ukhttp://www.xtremepapers.net/http://asphysics.edublogs.org/
- 7. A physical quantity is a physical property of a phenomenon, body, or substance, that can be quantified by measurement.E.g.: If the temperature T of a body is quantified (measured) as 300 kelvin this is written T = 300 x K = 300 K where T is the symbol for the physical quantity, and K is the symbol for the unit.What is a Physical Quantity
- 8. Physical Quantities are of two types:Base quantitiesDerived quantities
- 11. For Derived QuantitiesWhen you are asked to write the units of a derived quantity in terms of its “base units”, then you recall its respective formula:Example: Volume=l*b*h hence base units=mArea=l*l hence base units= mSpeed=distance/time hence base units=m/sTherefore; as a golden rule, you are just supposed to recall the base units of the 7 base quantities we talked about and the rest would all be provided in the Question.Till now, we talked about general units of derived quantities, that’s why we didn’t say that derived quantities have SI units (remember how I said that Volume can have the units of liters, m ,cm ,dm ). Now we will look at the concept of SI “base units” and their nexus with derived quantities. 33332The Base Units Concept
- 12. Recall how I said that the units on the LHS and the RHS of the equal sign should be the same: i.e. Suppose A=MD/CThe base units of A are Kgmsec /mM=kgD=mThen find the base units of the quantity C.Make C the subject:C=MD/A, C=kg*m/kgmsec /mC=m/secQ1. Units of acceleration.Q2. Find the units of Force using the formula: F=maQ3. Units of Pressure? P=pgh222
- 13. Labeling Graphs:X axis independent quantityY axis dependent quantity(Recall speed-time)Table Columns:Time
- 15. Class TestConvert the following quantities into different SI prefixes. Show your entire working. An answer without working would earn a straight ‘zero’ Use the symbols for the units in your answer. Use of the standard form where appropriate will earn you extra credit All questions carry 2 marks1. 145.56s to milliseconds (ms)2. 127845.64ms to seconds (s)3. 123923593426.2 microseconds (μs) to seconds (s)4. 67000.75 km to m5. 65.7mm to km6. 85.9km to mm7. 6.7m to μm (micrometer)8. 7800540032.54μm to km9. 7807.089J (joules) to MJ (mega joules)10. 6574.56 MJ to J
- 16. After you will be done with the A 'level syllabus, you will be in a position to give a rough estimate of quantities you have studied in your course. ‘Till now, you can give a rough estimate of quantities like:height of the door?diameter of pencil / pencil lead volume of brick / liquid in drinking cup mass of brick / person / nail time between your hiccups? Just to give you a feel of what kind of estimate questions you can see in your past papers:
- 17. May/June 2008, Paper 2, question 1
- 19. Thank youBe the Change that you want to witness in the World.
Editor's Notes
- #15: Talk about measuring instruments which work on different scales:Micrometers VCRulersMeasuring tapesEtc.
- #18: allow anything in range 20 Hz -> 20 kHz [we know that a bat produces and hears sounds btw 20000Hz to 120000Hz and elephants hear a frequency which is infrasonic- they communicate miles away with their peers at very low frequencies which we humans can not hear. This is 15 hz or less hence we say that audible range is 20Hz to 20KHz.]b. allow anything in range 10 nm -> 400 nmVisible light has a wavelength of 400-700nm so since UV radiations are on the right side of the EM spectrum and hence a greater frequency, Hence they should have a lesser wavelength so you can write anything below 400nm.c. allow anything in range 10 g -> 100 a tomato has a mass of 15-20 grams, so a big plastic ruler would be a bit less than a tomatoes mass and hence 10-15grams d. allow anything in range 0.1 kg m–3 -> 10 kg m–3Something between 1-5 kg/m-3, actually its 1.22kg/m-3 at sea level