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# 2) Resistance and Ohm's Law

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Short notes on electronics by Mand Labs

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### 2) Resistance and Ohm's Law

1. 1. www.mandlabs.com
2. 2. Mand Labs presents Current & Resistance
3. 3. Current • Current- Amount of charge (number of electrons ✕ charge on 1 electron) crossing through a particular section in one second • Why Electrons ﬂow- Potential difference & Closed Path • Direction of Current is taken as opposite to movement of electrons
4. 4. Current from battery • 9V Potential Difference • An external path/circuit between +ve and -ve • Current ﬂows from +ve terminal to -ve terminal • Direct Current (DC)
5. 5. • Unit of Current is Ampere • Ampere is expressed as A • Examples: 2.5 A, 3 A, 100 A, 423.55 A • Symbol is I • Current Rating- Max. current that you can safely pass through a device before you can fuse it Current
6. 6. Alternating Current • Does not mean just mean ﬂuctuating • Direction of current keeps changing • Both +ve and −ve voltage (or current) cycles in the current • Preferred for transmission and high voltages • Minimal Energy Loss in transmission • Examples: Air Conditioner, Electric Iron, Water Cooler run on AC
7. 7. Direct Current • Unidirectional current • Either complete +ve or -ve votlage (or current) cycles • Energy Loss is substantial • Preferred for low voltage applications • Examples: Car, Mobile Phone run on DC battery
8. 8. If ﬂoor is too smooth, you will not be able to walk. You need some roughness. In electricity, we can create friction to the ﬂow of current using a resistor. Resistor
9. 9. • Limits the ﬂow of current • Conductor: Offers less resistance to the ﬂow • Insulator: Offers inﬁnite resistance to the ﬂow • Eats away voltage and converts it into heat energy (joule heat) • Voltage drop- The voltage it eats away • Resistor offers Resistance Resistor
10. 10. • Main Uses: ‣ Control the amount of current in a circuit ‣ Divide voltage in a circuit • Unit is Ohm and expressed as Ω • Examples: 10R Ω, 10 kΩ, 10 MΩ, 4k7 Ω Resistor Schematic Symbol
11. 11. • Meanings: • 10R = 10 Ω • 10k = 10 Kilo = 10 × 1000 = 10,000 Ω • 10M = 10 Mega = 1000,000 = 10,000,000 Ω • 4k7 = 4.7k = 4.7 × 1000 = 4700 Ω • Remember: 1k (kilo) = 1000 = 103 and 1M (Mega) = 106 Units
12. 12. 1) Ist Band - Orange 2) 2nd Band - Orange 3) 3rd Band - Brown 4) 4th Band - Gold Color Coding Reading Resistance
13. 13. B B R O Y G B V G W Readﬁrstalphabetofcolor BB Roy Great BritainVery Good Wife Color Band Table
14. 14. Formula: 1st digit 2nd digit × 103rd digit ± y% No. Color Digit 1 Orange 3 2 Orange 3 3 Brown 1 4 Gold 5% 33 × 101 ± 5% = 330 Ω ± 5% ➡ First Color Band - 1st digit ➡ Second Color Band - 2nd digit ➡Third Color Band- 3rd digit ➡Fourth Color Band - y % ➡ y is known as Tolerance ➡Tolerance is the % by which the resistance value will vary Color Code Formula
15. 15. Another example No. Color Digit 1 Brown 1 2 Black 0 3 Orange 3 4 Gold 5% 10 × 103 ± 5% = 10,000 Ω = 10 kΩ
16. 16. Measure R using a Multimeter • Rotate the dial to Ω region • Set the appropriate range • Range Available: 200 to 2000k (2000k = 2000,000) • If the dial is on 20k or 200k or 2000k, multiply the meter reading by 1000 to get the actual value • If you get 1 on the left hand side of the display, increase the range
17. 17. Steps to measure R • Set the meter dial to 2000 in Ω region • Connect the probes across the two legs of the resistor • A resistor does not have any +ve and -ve Multimeter Reading = 330 Ω Color Code - Orange Orange Brown Gold
18. 18. Example: Color Code • Pick up a resistor with color code: Brown Black Orange Gold • Meter shows reading 1 on the 2000 Ω range • Increase the range to 20k (in next slide)
19. 19. Example: Measure R • Note down the reading • Since the meter dial is on 20k, multiply the reading with 1k = 1000 to get the actual value Reading = 10.07, Value = 10.07 × 1000 = 10 kΩ
20. 20. Ohm’s Law • Deﬁnes relation betweenV (voltage), R (resistance) and I (current) • R =V/I = constant (ratio is constant) • Voltage = Current × Resistance • V = R I • Example: If V = 9V, R = 1 kΩ • I =V/R = 9/1000 = 0.009 A = 9 mA (1milli = 1m = 1/1000)
21. 21. Ohm’s Law Triangle
22. 22. www.mandlabs.com