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Questions and Answers
Which of the following is NOT a base unit in the SI system?
Which of the following is NOT a base unit in the SI system?
What makes metric units easy to use?
What makes metric units easy to use?
What is the SI unit for resistance?
What is the SI unit for resistance?
What does the prefix 'kilo-' mean?
What does the prefix 'kilo-' mean?
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Which of the following is NOT a factor that affects resistance?
Which of the following is NOT a factor that affects resistance?
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What is the relationship between voltage, current, and resistance as described by Ohm's Law?
What is the relationship between voltage, current, and resistance as described by Ohm's Law?
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How is current measured?
How is current measured?
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How is voltage measured?
How is voltage measured?
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An open circuit is characterized by zero current flow and infinite resistance.
An open circuit is characterized by zero current flow and infinite resistance.
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A short circuit is characterized by infinite current flow and zero resistance.
A short circuit is characterized by infinite current flow and zero resistance.
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Study Notes
IT 219 Physics for IT
- The course covers Physics for IT, specifically analogue circuits.
- Lecture 1 focuses on analogue circuits, part 1.
Outline
- The outline includes units for measurements (English and SI systems).
- Analogue circuits (part 1) covers voltage, current, resistance, Ohm's law, and measuring current and voltage.
Measurement
- Measuring involves comparing an object's dimension to a standard using a measuring tool.
- Examples include checking weight, reading a watch, taking temperature, and weighing fruits.
Standards of Measurement
- Measurement uses a measuring tool to compare an object's dimension to a standard.
Tools for Measurement
- Tools used for measurements include measuring cylinders, stopwatches, thermometers, and scales.
Learning Check: Tools for Measurements
- Tools for measuring temperature: thermometer.
- Tools for measuring volume: measuring cup and graduated cylinder.
- Tools for measuring time: watch.
- Tools for measuring weight: scale.
Learning Check: English System
- Units for length: inch, foot, yard, mile.
- Units for volume: cup, teaspoon, gallon, pint, quart.
- Units for weight: ounce, pound, ton.
- Units for temperature: °F.
Using International System of Units (SI)
- SI units are based on multiples of 10, making conversions easier.
- Measurements in SI units are easily understood by scientists and are easier to convert than English units.
- SI metric system was established in France in 1795.
- The SI system is a revised version of the metric system, adopted in 1960.
- The SI system is used internationally.
The SI System
- Base units include meter (m), gram (g), liter (L), second (s), ampere (A), and Celsius (°C).
- Derived units include joule (J) for work/energy and watt (W) for power (1W= 1J/s).
Measurement System Comparisons
- A table comparing English and SI units in length, mass, volume, temperature and time.
Using SI Units of Length
- The base unit of length in SI is the meter (m).
- For large and small measurements, prefixes like kilo- and milli- are used.
Using SI Units - Prefixes of Common Use
- A table listing commonly used prefixes and their corresponding factors.
Includes prefixes like Giga, Mega, Kilo, Deci, Centi, Milli, Micro, Nano, and Pico.
Using SI Units
- Example: 12.3 mW = 0.0123 W = 1.23 x 10-2 W
- For large distances, kilometers (km) are used. 1 km = 1000 m.
Stating a Measurement
- Measurements include a number and a unit.
Learning Check: Units of Measurement
- Units for examples include:
- Temperature: °F (degrees Fahrenheit).
- Weight: lbs (pounds).
- Distance: miles.
- Volume: L (liters).
Learning Check: SI Metric Units
- Identifying measurements in SI metric units:
- John's height: 2 meters.
- Saline volume: 1 liter.
- Lemon mass: 145 grams.
Analogue Circuits – Part 1
- Electricity is the flow of charges (electrons).
- A circuit is a path for electrons to flow.
- Electrons flow only in complete circuits (closed circuits).
- Open circuits have gaps, preventing electron flow.
A Basic Circuit
- All electrical circuits have three main parts: a source of energy, a closed path, and a device using the energy.
- An open circuit will prevent any device from working.
Would This Work?
- A closed circuit (allowing flow) would work.
Voltage
- Voltage measures potential energy causing current flow.
- Voltage is a difference (compared to a 'ground' point).
- Voltage is also known as electromotive force (EMF).
Potential Difference = Voltage = EMF
- Chemical reactions in a battery transfer electrons, creating a potential difference (voltage).
- The maximum potential difference is called the electromotive force (EMF), which is essentially the energy per charge (in volts).
Why Does Current Flow?
- A voltage source provides energy/work to generate current.
- Voltage raises the potential energy of charged particles (usually electrons), causing them to flow from one terminal to a device, then back to the source.
Current and Charge
- Current is the rate of charge flow (measured in amperes – A).
- 1 ampere = 1 coulomb/second.
- Current is only measurable in complete circuits (closed).
Current (I)
- An electron has a charge of -1.602 x 10−19 Coulombs.
- Current is the rate of flow of charged particles (electrons).
- Current is calculated by multiplying the number of electrons passing per second by the electron's charge.
Electron Flow Vs Current Flow
- Electron flow is opposite to conventional current flow.
Types of Current
- DC: Direct current moves in one direction (e.g., battery).
- AC: Alternating current reverses direction periodically (e.g., wall outlet).
AC and DC Current
- DC current is constant.
- AC current changes sinusoidally.
Circuit Elements – The Resistor
- A resistor opposes electrical current flow.
- The unit of resistance is the ohm (Ω).
Resistance
- Resistance depends on material, geometry (shape), length, cross-sectional area, and temperature.
Factors Affecting Resistance
- Resistance is directly proportional to length (longer = higher resistance).
- Resistance is inversely proportional to cross-sectional area (larger area = less resistance).
- Higher temperatures generally increase resistance.
- Certain materials have more resistance than others.
Resistors
- Description of various physical resistor forms.
Ohm's Law
- Voltage is directly proportional to current when resistance is constant. - V = IR
- Resistance is the slope of a voltage-current graph.
Ohm's Law
- I = V/R (Current equals Voltage divided by Resistance).
- I (current) is in amperes (Amps), V (voltage) is in volts (V), and R (resistance) is in ohms (Ω).
Example
- For a 560 Ω resistor with a current of 42.4 mA, the voltage is 23.7 V.
Measuring Current
- Current is measured in amps (A) using an ammeter connected in series with the circuit.
Measuring Voltage
- Voltage is measured in volts (V) using a voltmeter connected across the element.
The Voltmeter and Ammeter
- Voltmeters measure voltage across a circuit element.
- Ammeters measure current through a circuit element.
Open and Short Circuits
- Open circuit: no current (i = 0), infinite resistance (R = ∞).
- Short circuit: zero voltage (v = 0), zero resistance (R = 0), any current.
Circuit Schematic Diagrams
- Symbols for various circuit components (wired, batteries, resistors, capacitors, switches, lamps).
- Specific symbols used to show positive/negative for a battery.
Simple Circuit
- How to draw a simple circuit.
Self-Reading
- Assigned textbook sections for further study specifically on electric current, resistance, resistivity, and the use of ammeters and voltmeters.
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Description
This quiz focuses on the fundamentals of analogue circuits as part of the IT 219 Physics for IT course. It covers key concepts including voltage, current, resistance, and the tools necessary for measurement, helping students solidify their understanding of measurement standards and techniques in physics.
