"Measurement of Current" Current and Circuit PPT Teaching Courseware

Description

"Measurement of Current" Current and Circuit PPT Teaching Courseware

Part One: Knowledge Management

1. current

Definition: A physical quantity that represents the strength of an electric current. I represents the electric current.

Unit: In the International System of Units, the unit of electric current is ampere, referred to as ampere (A). Commonly used units of current include milliamps (mA) and microamps (μA). 1 A=1 000 mA, 1 mA=1 000 μA.

2. Ammeter

Usage: three must, two don’t, two see clearly, one try and touch.

Three important points: ① Adjust to zero; ② Make the current flow in from the "+" terminal and flow out from the "-" terminal; ③ Connect the ammeter in series in the circuit to be measured.

Two nos: ① The current in the circuit to be measured should not exceed the range of the ammeter; ② Do not connect the ammeter directly to the two poles of the power supply.

2. See clearly: ① See the range clearly; ② See the graduation value clearly.

One test touch: In order to avoid damaging the ammeter due to excessive current, if the current cannot be estimated in advance, you can first close the switch and then quickly contact and disconnect (test touch) to see if the deflection of the pointer is at the maximum at the moment the switch is closed. within the measured value.

Note: Do not connect the ammeter directly to the two poles of the power supply under any circumstances. This will cause a short circuit and burn out the ammeter.

Current measurement PPT, part 2: classification and exploration

Type one: Connection of ammeter

[2017•Hunan Huaihua]In the figure, the circuit that can directly measure the current through the lamp L1 is ()

[Analysis] In picture A, the ammeter is on the main circuit, and the ammeter measures the main circuit current, so A is wrong; in picture B, the ammeter is connected in series with L1, but the positive and negative terminals of the ammeter are reversed, and the current of L1 cannot be measured, so B is wrong; In Figure C, two light bulbs are connected in parallel, and the ammeter is connected in series with L2. The ammeter measures the current of the L2 branch and cannot directly measure the current through lamp L1, so C is wrong; in Figure D, the ammeter is connected in series with L1, and the positive and negative terminals of the ammeter are wired correctly. The current through lamp L1 can be measured directly, so D is correct.

[Methods and Tips] To answer this kind of question, you only need to grasp which electrical appliance the ammeter is to measure current and connect it in series with that electrical appliance, and the current must flow in from the positive terminal of the ammeter and flow out from the negative terminal.

Type 2: Ammeter readings

A certain ammeter has two ranges. It is only known that the large range is 0~9 A, and the scale value of the small range is not marked. In order to find out what the small range of the ammeter is, Wang Qiang first used the large range to measure a smaller current, and the reading was as shown in Figure A, and then switched to the small range to measure the same current, with the pointer pointing at the position of Figure B.

(1)The current value he measured was ______A.

(2) Fill in the small range numbers corresponding to the large range numbers in the table below.

[Analysis] The large range is 0~9 A, a large grid represents 3 A, and the graduation value is 1.5 A. When two ranges measure the same current, the indication of the large range is 1.5 A, the indication of the small range is also 1.5 A, and the graduation value is 0.5 A. The graduation value of the large range is 3 times that of the small range, so The value corresponding to the large range is also three times the value corresponding to the small range.

[Methods and Tips] Correct reading of ammeter: First determine the range used by the ammeter, and then determine the indication represented by each large grid and each small grid. There are two ranges on the same dial. Selection of ammeter range: ① Estimate the size of the current in the circuit under test; ② If it cannot be estimated, touch the switch in the circuit to the large-range terminal; ③ If the measured current exceeds the small range, select a larger range; If it is within a smaller range, use the smaller range, and the smaller range is chosen to reduce the error in readings.

Current measurement PPT, the third part: evaluation in class

1. The current of a household refrigerator during normal operation is approximately ()

A. 1 μA B. 1A

C. 1×105 A D. 1 mA

2. [2019•Qingdao, Shandong]As shown in the figure, the reading of the ammeter (range 0.6 A) is ()

A. 0.2 A B. 0.52A

C. 1.2 A D. 0.3 A

3. [2019•Shandong Dezhou]As shown in the picture, after Xiao Ming completed the circuit connection and closed the switch, he found that the ammeter pointer deflected to the left of the zero scale line. The reason may be ()

A. The current is too large and exceeds the measurement range.

B． The positive and negative terminals of the ammeter are connected reversely

C. The ammeter is connected in parallel to both ends of the electrical appliance.

D． Current is too small

4. [2017•Hangzhou, Zhejiang]When a student used an ammeter to measure current, he selected the range of 0 to 0.6 A based on the estimate of the current to be measured in the circuit, but he mistakenly mistook the "-" and " 3" two terminals are connected to the circuit. The result of this is ()

A. The angle of pointer deflection increases

B． The pointer does not move

C. May burn out the ammeter

D． The pointer deflection angle is reduced

5. [2019•Heilongjiang Harbin]Which of the following methods of using ammeter is wrong ()

A. Zero adjustment before use

B． Do not connect the ammeter directly to the two poles of the power supply

C. The ammeter should be connected in parallel in the circuit

D． The measured current cannot exceed the range of the ammeter

Current measurement PPT, part 4: layered operations

1. [2018•Guangxi Guigang]Among the following household appliances, the one with the highest current during normal operation is ()

A. Washing machine b. TV set

C. Air conditioning D. refrigerator

2. [2019•Nanjing, Jiangsu]The experimental circuit of "Measuring current with an ammeter" is shown in the figure. Among them, the one that can correctly measure the current in the small light bulb L1 is ()

[Analysis] After the switch in A is closed, the two light bulbs are connected in parallel, and the ammeter measures the current in the main circuit, so A is wrong; after the switch in B is closed, the two light bulbs are connected in series, but the current flows in from the negative terminal of the ammeter and flows out from the positive terminal. The connection method is wrong, so B is wrong; after the switch in C is closed, the two bulbs are connected in parallel, the ammeter is connected in series with L1, and the positive and negative terminals of the ammeter are connected correctly, and the current in the small bulb L1 can be measured correctly, so C is correct; D After the switch is closed, the ammeter is connected in parallel with the lamps L1 and L2, and L1 and L2 are short-circuited, so D is wrong.

3. [2017•Zhejiang Ningbo]A student chose an ammeter with the "0~3 A" range to measure the current, while another student measured the current with the "0~0.6 A" range. The reading was 0.48 A, so the actual The current measured on should be ()

A. 24 A B. 2.4A

C. 0.24 A D. 0.48 A

4. [2019•Guangxi Fangchenggang]When learning how to use an ammeter, you should first observe the ammeter and draw the following conclusions. Which one do you think is wrong ()

A. At this time, the current passing through the ammeter is 1.0 A

B． This ammeter is a dual-range ammeter

C. When using a terminal with a range of 0 to 3 A, the graduation value is 0.1 A

D． The ammeter should be zeroed before use

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For more information about the "Measurement of Current and Circuit Current" PPT courseware, please click the "Measurement of Current in Current and Circuit ppt" ppt tag.

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Update Time: 2024-07-26

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