Lesson Notes By Weeks and Term v4 - SHS 1
INTRODUCTION TO PHYSI CS
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INTRODUCTION TO PHYSI CS
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Subject: Physics
Class: SHS 1
Term: 1st Term
Week: 4
Grade code: 1.1.1.LI.3
Strand code: 1
Sub-strand code: 1
Content standard code: 1.1.1.CS.2
Indicator code: 1.1.1.LI.3
Theme: MECHANICS AND MATTER
Subtheme: INTRODUCTION TO PHYSI CS
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In our daily lives in Ghana, from the seamstress in Makola measuring fabric for a new school uniform, to the carpenter in Sunyani crafting a new desk, to the lab technician at Korle Bu measuring medicine, accuracy is extremely important. A small mistake in measurement can lead to a dress that doesn't fit, a wobbly table, or the wrong dose of medication. In physics, accurate measurement is the foundation of all experiments and discoveries. Today, we will learn about the common mistakes, or "errors," that can happen when we use measuring instruments, and more importantly, how to identify and avoid them.
A. What is a Measurement Error?
A measurement error is the difference between a measured value of a quantity and its true, or actual, value. It is not just a "mistake" in the everyday sense; it's an unavoidable part of measurement. Our goal is to understand these errors so we can minimise them.
There are two main types of errors we will discuss later, but for today, we focus on identifying the specific errors associated with common laboratory instruments. B. Errors in Using the Meter Rule
A meter rule is one of our most basic instruments, but errors are still common. Parallax Error: This is the most common error. It occurs when the observer's eye is not positioned directly perpendicular to the measurement mark on the scale. Viewing the scale from an angle makes the reading appear shifted. How to Identify: If two people look at the same measurement from different angles, they will get slightly different readings. How to Avoid: Always position your eye directly above the mark you are reading. Your line of sight should be at a 90° angle to the ruler's surface. Zero Error / End Error: This occurs when the zero mark of the ruler is not aligned with the start of the object being measured. This can be because the end of the ruler is worn out or damaged. How to Identify: Look at the "0" mark on the ruler. Is it clear and exactly at the end? If not, there is a potential for end error. How to Avoid: Start your measurement from a clear, whole number mark (like 1 cm) instead of the damaged end. Remember to subtract that starting value from your final reading. Example: To measure a pencil, you align its tip with the 1 cm mark. The other end reads 16.5 cm. The actual length is 16.5 cm - 1.0 cm = 15.5 cm. C. Errors in Using the Protractor Parallax Error: Just like with a meter rule, reading the angle from the side instead of directly above will cause an incorrect reading. Incorrect Placement: This error occurs if the protractor is not positioned correctly. The centre point (or crosshair) of the protractor must be placed exactly on the vertex (the corner) of the angle being measured. The baseline (0° line) of the protractor must be aligned perfectly with one of the arms of the angle. How to Identify: Check the placement. Is the vertex at the centre? Is the 0° line lying flat on one of the angle's lines? If not, the reading is wrong. D. Errors in Using the Electronic Balance Zero Error: This happens when the balance does not show a reading of "0.00 g" before any object is placed on it. This is the most common error. How to Identify: Look at the display before placing your sample. If it shows any value other than zero, there is a zero error. How to Avoid: Always press the "TARE" or "ZERO" button before taking a measurement. If you are measuring a substance in a container (like gari in a bowl), place the empty bowl on the balance first, press "TARE" to reset it to zero, and then add the gari. The balance will then show only the mass of the gari. Environmental Errors: Air currents: A breeze from a fan or an open window can press down on the pan, affecting the reading. Use the balance in a draft-free area. Vibrations: Placing the balance on an unstable bench can cause the reading to fluctuate. Ensure it is on a solid, level surface. E. Errors in Using the Vernier Caliper