14 - SAFETY: THE OHMMETER AND COLOR CODING

Question 1

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.

Answer 1

electricity

Question 2

Currents flowing through one’s body can cause serious ____________. The effects vary with the amount of ____________ of a person.

Answer 2

physiological damage
resistance

Question 3

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.

Question 4

an instrument for measuring resistances.

Answer 4

ohmmeter

Question 5

OBJECTIVES: (3)

Answer 5

1. To learn how to use the multitester as an ohmmeter
2. To learn simple safety rules when dealing with electricity
3. To learn to read resistor color-coding

Question 6

To use it as an ohmmeter, turn the function switch to the

Answer 6

ohmmeter function (with symbol Ω).

Question 7

If the magnitude of the resistance to be measured is unknown, set the function switch to the __________

Answer 7

highest range

Question 8

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.

Answer 8

red = positive (+)
black = negative (-)

b.) Short the test leads, 0Ω-adjust knob

c.) turn off the power of the circuit and discharge capacitors

Question 9

__________ current is lethal

Answer 9

100 mA(or 0.1 A)

Question 10

voltage formula

Answer 10

V = Current (A) x Resistance (R)

Question 11

_________ are electronic components commonly used in electronic instruments.

Answer 11

Resistors

Question 12

Their resistances are usually determined by the ____________ indicated. Below is the color code table for resistors.

Answer 12

colors of the four (or sometimes three) bands

Question 13

The ________ band represents the multiplier and the _________ band (sometimes absent) is the tolerance of the resistor.

Answer 13

third
last

Question 14

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%

Answer 14

BBROYGBVGWGS

Black
Brown
Red
Orange
Yellow
Green
Blue
Violet
Gray
White
Gold
Silver

Question 15

Under what condition will one have a greater possibility of being electrocuted? Why?

Answer 15

if wet, lower resistance

Question 16

What happened to the resistance measurement when you held the test leads tighter?

Answer 16

decreases

Question 17

On which half of the uppermost scale will resistances be accurately measured? Why?

Answer 17

right half, many minor divisions allowing fine readings

Question 18

What can you say about resistance measurements if one has not shorted the test leads before the measurements were made?

Answer 18

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.

Question 19

Using the ohmmeter, how can you determine the continuity of a switch?

Answer 19

if it shows 0 = switch is on (continuity)
resistance is infinite = switch is off (open)