## Ammeter and Voltmeter

1. Ammeters are measuring instrument used to measure electric current.
2. Voltmeters are measuring instrument used to measure potential difference (voltage).
3. In SPM syllabus, you need to know
1. how to take reading from ammeter and voltmeter
2. how to identify the sensitivity of an ammeter and voltmeter.
3. the connection of ammeter and voltmeter in a circuit.
4. An ammeter is always connected in series with the load (resistor) in a circuit.
5. A voltmeter is always connected parallel to the load (resistor) in a circuit.

## Micrometer Screw Gauge

Label of the Parts

(This image is licienced under GDFL. The source file can be obtained from wikipedia.org)

### Range and Accuracy

1. The range of a micrometer is 0-25mm.
2. The accuracy of a micrometer is up to 0.01mm.

### How to Use a Micrometer?

1. Turn the thimble until the object is gripped gently between the anvil and spindle.
2. Turn the ratchet knob until a “click” sound is heard. This is to prevent exerting too much pressure on the object measured.

Reading of main scale = 0 – 25 mm
Reading of thimble scale = 0 – 0.49mm

Example

Reading of main scale = 5.5mm
Reading of thimble scale = 0.28mm

Actual Reading = 5.5mm + 0.28mm = 5.78mm

### Precaution Steps

1. The spindle and anvil are cleaned with a tissue or cloth so that any dirt present will not be measured.
2. The thimble must be tightened until the first click is heard.
3. The zero error is recorded.

Interactive Animation
SHAW : micrometer (Java Applet)

The Micrometer – Upscale.Utoronto.ca

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## Vernier Caliper

1. Vernier calliper is a measuring tool used to measure length.
2. It is more accurate than the metre rule. It can measure the length with an accuracy up to 0.01cm.
3. The figure above shows the illustration of a vernier calliper. For SPM students, you need to remember the name of the parts and the function of the 2 jaws and the stem.

### Taking Reading from a Vernier Calipers:

1. A vernier calliper has 2 scales, namely the main scale and the vernier scale.
2. The main scale is read at the zero mark of the Vernier scale.
3. The vernier scale is read at the point where it’s scale coincide with the main scale.
5. The vernier scale is 9mm long, divided into 10 divisions.

Example:

Reading of main scale = 2.2cm
Reading of vernier scale = 0.07cm
Reading of the vernier calliper = 2.27cm

### Zero Error of Vernier Caliper

1. The zero error is determined by tightening the jaws of the vernier callipers.
2. Zero error must be eliminated from the reading.

Example:
Images below show the reading of 3 vernier callipers when their jaws are tightly closed. Find the zero error of each calliper.
a.

Zero error = 0.02 cm

b.

Zero error = -0.06cm

c.

Zero error = 0 cm (No zero error)

## Ruler, Thermometer and Stopwatch

### Ruler

A metre rule has sensitivity or accuracy accuracy of 1mm.
Precaution to be taken when using ruler

1. Make sure that the object is in contact with the ruler.
2. Avoid parallax error.
3. Avoid zero error and end error.

### Thermometer

There are 2 types of mercury thermometer

1. Thermometers of range -10oC – 110oC with accuracy 1oC.
2. Thermometers of range 0oC – 360oC with accuracy 2oC.

Precaution to be taken when using a thermometer

1. Make sure that the temperature measured does not exceed the measuring range.
2. When measuring the temperature of a liquid
1. immerse the bulb fully in the liquid
2. stir the liquid so that the temperature in the liquid is uniform
3. do not stir the liquid vigorously to avoid breaking the thermometer

### Stopwatch

There are 2 types of stopwatches

1. analogue stopwatches of sensitivity 0.1s or 0.2s
2. digital stopwatches of sensitivity 0.01s.

The sensitivity of a stopwatch depends on the reaction time of the user.

## Consistency, Accuracy and Sensitivity

### Precision

1. Precision is the ability of an instrument in measuring a quantity in a consistent manner with only a small relative deviation between readings.
2. The precision of a reading can be indicated by its relative deviation.
3. The relative deviation is the percentage of mean deviation for a set of measurements and it is defined by the following formula:

### Accuracy

1. The accuracy of a measurement is the approximation of the measurement to the actual value for a certain quantity of Physics.
2. The measurement is more accurate if its number of significant figures increases.
3. Table above shows that the micrometer screw gauge is more accurate than the other measuring instruments.

1. The accuracy of a measurement can be increased by
1. taking a number of repeat readings to calculate the mean value of the reading.
2. avoiding the end errors or zero errors.
3. taking into account the zero and parallax errors.
4. using more sensitive equipment such as a vernier calliper to replace a ruler.
2. The difference between precision and accuracy can be shown by the spread of shooting of a target (as shown in the Diagram below).

### Sensitivity

1. The sensitivity of an instrument is its ability to detect small changes in the quantity that is being measured.
2. Thus, a sensitive instrument can quickly detect a small change in measurement.
3. Measuring instruments that have smaller-scale parts are more sensitive.
4. Sensitive instruments need not necessarily be accurate.

## Measurement and Error

### Error

1. Error is the difference between the actual value of a quantity and the value obtained in measurement.
2. There are 2 main types of error
1. Systematic Error
2. Random Error

### Systematic Error

1. Systematic errors are errors which tend to shift all measurements in a systematic way so their mean value is displaced. Systematic errors can be compensated if the errors are known.
2. Examples of systematic errors are
1. zero error, which cause by an incorrect position of the zero point
2. an incorrect calibration of the measuring instrument.
3. consistently improper use of equipment.
3. Systematic error can be reduced by
1. Conducting the experiment with care.
2. Repeating the experiment by using different instruments.

#### Zero error

1. A zero error arises when the measuring instrument does not start from exactly zero.
2. Zero errors are consistently present in every reading of a measurement.
3. The zero error can be positive or negative.

(NO ZERO ERROR: The pointer of the ammeter place on zero when no current flow through it.)

(NEGATIVE ZERO ERROR: The pointer of the ammeter does not place on zero but a negative value when no current flow through it.)
(POSITIVE ZERO ERROR: The pointer of the ammeter does not place on zero but a negative value when no current flow through it.)

#### Random errors

1. Random errors arise from unknown and unpredictable variations in condition.
2. It fluctuates from one measurement to the next.
3. Random errors are caused by factors that are beyond the control of the observers.
4. Random error can cause by
1. personal errors such as human limitations of sight and touch.
2. lack of sensitivity of the instrument: the instrument fail to respond to the small change.
3. natural errors such as changes in temperature or wind, while the experiment is in progress.
4. the wrong technique of measurement.
5. One example of random error is the parallax error. Random error can be reduced by
2. find the average value of the reading.

#### Parallax error

A parallax error is an error in reading an instrument due to the eye of the observer and pointer are not in a line perpendicular to the plane of the scale.