Physics 7 Lesson 24: Amperage
1. Summary of theory Tóm
An ammeter is an instrument for measuring electric current.
– Symbols: A and mA
– When using an ammeter to measure amperage, attention should be paid to:
Choose an ammeter with a GHG suitable for the results to be measured, the smaller the DCN ammeter, the higher the accuracy of the measurement results.
Connect the (+) pin of the ammeter to the positive pole of the power supply, do not connect the (+) , (-) pin of the ammeter directly to the two poles of the power supply.
The symbol for drawing a circuit diagram is:
1.3. Measure amperage
– When using ammeter, note:
- Select the ammeter with the smallest measurement limit and division suitable for the value to be measured.
- Connect the ammeter in series to the circuit to be measured amperage so that the current enters the positive (+) pin and exits the (-) pin of the ammeter (ie the (+) pin of the ammeter is connected to the positive terminal. of the power supply and the pin (-) of the ammeter is connected to the negative terminal of the power supply).
– The reading of the ammeter connected in an electrical circuit is the value of the amperage in that circuit.
– Do not connect the two pins of the ammeter directly to the two terminals of the power supply.
2. Illustrated exercise
2.1. Form 1: Convert the unit of amperage
Convert units for the following values:
a. 0.175 A = … mA
b. 0.38 A = … mA
c. 1250 mA=… A
d. 280 mA =… A.
We have: 1 mA = 0.001 A
1A = 1000 mA
a) 0.175 A = 175 mA
b) 0.38 A = 380 mA
c) 1250 mA = 1.25 A
d) 280 mA = 0.28 A
2.2. Form 2: Determine the right ammeter to use
There are four ammeters with the following measuring limits:
1) 2 mA
2) 20 mA
3) 250 mA
4) 2 A
Indicate which ammeter is best suited to measure each of the following amperages:
a. 15 mA
b. 0.15 A
c. 1,2 A.
If you choose an ammeter with a GHD much larger than the amperage to be measured, the measurement will be less accurate.
If you choose an ammeter with a GHD smaller than the amperage to be measured, the ammeter will be damaged (burned).
Therefore, we should choose an ammeter with a GHD larger than the amperage to be measured.
Select ammeter 2) 20 mA is best suited for measuring current a) 15 mA
Select ammeter 3) 250 mA is most suitable for measuring current b) 0.15 A
Select ammeter 4) 2 A is most suitable for measuring current c) 1.2 A
A 2 A voltmeter can be chosen to measure 15 mA or 0.15 A, but reading the ammeter reading will be less accurate because 2 A is much larger than 15 mA or 0.15 A.
3.1. Essay exercises
Question 1: Comment on the relationship between the brightness of the lamp and the intensity of the current through the lamp: The more current flows through the lamp, the more …… the more the lamp …….?
Verse 2: Using an ammeter with a measuring limit of 5A, the dial is divided into 25 smallest intervals. When measuring amperage in a circuit, the indicator needle is only about the 16th. The measured amperage is
Question 3: On one fuse it says 1A. What does this number mean?
Verse 4: What is the symbol for amperage?
3.2. Multiple choice exercises Bài
Question 1: Which of the following ammeters is best suited to measure the amperage flowing through the flashlight bulb (A maximum current of 0.35A is allowed).
A. Ammeter has a measuring limit of 1 A.
B. Ammeter with measuring limit of 0.5 A
C. Ammeter with measuring limit of 100 mA
D. Ammeter with measuring limit of 2 A
Verse 2: The relationship between the reading of the ammeter and the brightness of the lamp is stated by 4 students as follows. Which statement below is incorrect?
A. The light is not lit when the ammeter reading is very small.
B. The brighter the light, the larger the ammeter reading.
C. The reading of the ammeter decreases, the brightness of the lamp decreases.
D. The reading of the ammeter and the brightness of the lamp have nothing to do with each other.
Question 3: When connecting an ammeter to a circuit, what should be paid attention to?
A. The negative pin of the ammeter is connected to the positive terminal of the power supply and the positive pin is connected to the light bulb.
B. Do not connect the two pins of the ammeter directly to the mains.
C. The positive pin of the ammeter is connected to the negative terminal of the power supply and the negative pin is connected to the light bulb.
D. Connect the ammeter’s two pins directly to the two terminals of the power supply.
Verse 4: Ammeter is an instrument to measure:
B. voltage difference
C. electric capacity
Through this lecture, students need to complete some of the objectives given by the lesson, such as:
The stronger the current, the greater its magnitude and the stronger the effect of the current
State that the unit of electric current is the ampere, symbol A.
Use an ammeter to measure amperage (select the appropriate ammeter and connect the correct ammeter)