14 - SAFETY: THE OHMMETER AND COLOR CODING Flashcards
This activity will be dealing with ________. Although the voltages used in the experiments are not lethal to a normal person, shocks may occur at some instances.
electricity
Currents flowing through one’s body can cause serious ____________. The effects vary with the amount of ____________ of a person.
physiological damage
resistance
It is important to learn how certain conditions affect body resistance so that we may be aware of what to avoid and find means of dealing with electricity safely.
an instrument for measuring resistances.
ohmmeter
OBJECTIVES: (3)
- To learn how to use the multitester as an ohmmeter
- To learn simple safety rules when dealing with electricity
- To learn to read resistor color-coding
To use it as an ohmmeter, turn the function switch to the
ohmmeter function (with symbol Ω).
If the magnitude of the resistance to be measured is unknown, set the function switch to the __________
highest range
The succeeding steps are as follows:
a) Connect the red test lead to the ________ terminal and the black test lead to the _________ terminal.
b.) ________________ so that the needle will deflect from left to right until it reaches the zero mark of the uppermost scaling of the meter. If the needle does not point to zero, rotate the ____________ until the needle points to the zero mark.
c.) Connect the test probe end-to-end to the resistance being measured. If the resistance to be measured is connected to a circuit, ____________________ and _____________ before connecting test leads. Setting the range switch to the appropriate range increases the accuracy of the reading.
d.) Every time you change the range, repeat step b.
e.) Determine the resistance of 5 resistors using the ohmmeter.
red = positive (+)
black = negative (-)
b.) Short the test leads, 0Ω-adjust knob
c.) turn off the power of the circuit and discharge capacitors
__________ current is lethal
100 mA(or 0.1 A)
voltage formula
V = Current (A) x Resistance (R)
_________ are electronic components commonly used in electronic instruments.
Resistors
Their resistances are usually determined by the ____________ indicated. Below is the color code table for resistors.
colors of the four (or sometimes three) bands
The ________ band represents the multiplier and the _________ band (sometimes absent) is the tolerance of the resistor.
third
last
Color
DIGIT, MULTIPLIER, TOLERANCE
0,1
1,10^1
2,10^2
3,10^3
4,10^4
5,10^5
6,10^6
7,10^7
8,10^8
9,10^9
_,10^-1, 5%
_,10^-2, 10%
BBROYGBVGWGS
Black
Brown
Red
Orange
Yellow
Green
Blue
Violet
Gray
White
Gold
Silver
Under what condition will one have a greater possibility of being electrocuted? Why?
if wet, lower resistance
What happened to the resistance measurement when you held the test leads tighter?
decreases
On which half of the uppermost scale will resistances be accurately measured? Why?
right half, many minor divisions allowing fine readings
What can you say about resistance measurements if one has not shorted the test leads before the measurements were made?
If you don’t short the test leads before measuring resistance, the resistance of the leads themselves and any contact resistance at the measurement points can affect the accuracy of your reading because these resistances add to the total measured value. This is especially important when measuring low resistances, as the meter may not be able to distinguish between the actual resistance and the additional resistance from the leads or contact points, leading to inaccurate results.
Using the ohmmeter, how can you determine the continuity of a switch?
if it shows 0 = switch is on (continuity)
resistance is infinite = switch is off (open)
