"Ohm's Law" Ohm's Law PPT download

"Ohm's Law" Ohm's Law PPT download

Part One Content: Basic Knowledge Key Points

Knowledge point 1 Ohm’s law

1. German physicist Ohm began to study the relationship between current, power supply and wire length in 1825, and in 1826 he summarized what is known today as Ohm’s law, that is, the current in a conductor is proportional to the voltage at both ends of the conductor. Inversely proportional to the resistance of the conductor.

2. The formula R=?/? can be derived from Ohm’s law. The correct one of the following statements is (D)

A. When the voltage increases by 2 times, the resistance R increases by 2 times

B. When the current increases by 2 times, the resistance R decreases by 2 times.

C. When the voltage is zero, the resistance R is zero

D. No matter what the voltage or current is, the resistance of the resistor remains unchanged.

Knowledge Point 2 Application of Ohm’s Law

3. (Anhui High School Entrance Examination) When a voltage of 10 V is applied to both ends of a fixed-value resistor, and the current passing through it is measured to be 2 A, then its resistance is 5Ω. If the voltage is 0, then its resistance is 5 Ω.

4. (Zigong High School Entrance Examination) Two resistors A and B have resistance values ​​of 20 Ω and 40 Ω respectively. If they are connected in series to the circuit, the ratio of the voltages at both ends of resistors A and B is 1:2; connect them in parallel. When connected to the circuit, the ratio of currents passing through resistors A and B is 2:1.

5. The resistance of a certain light bulb when it is working is 20 Ω. The current passing through it is measured with an ammeter to be 0.6 A. Then the voltage across the light bulb is (B)

A.6 V B.12 V C.18 V D.24 V

6. The relationship between the current in a conductor and the voltage across it is shown in the figure. The following statement is correct (C)

A. The voltage across the conductor decreases as the current increases

B. The resistance of the conductor decreases as the voltage increases

C. When the voltage across the conductor is 0, the resistance is 5 Ω

D. When the voltage across the conductor is 2 V, the current is 0.6 A

Ohm's Law PPT, Part 2: Improvement of Comprehensive Ability

7. As shown in the figure, the power supply voltage remains unchanged. When switches S1 and S2 are closed, the voltage indicates 6 V and the current indicates 0.3 A. After S2 is disconnected, the current indicates 0.2 A, and the power supply voltage is 6 The resistance of V and R2 is 10Ω.

8. (Anshun High School Entrance Examination) As shown in the figure, the power supply voltage is constant, R1=30 Ω, R2=60 Ω. When switch S3 is closed and S1 and S2 are both open, the ammeter reads 0.1 A, then the power supply voltage is 9 V ;When switch S3 is open and S1 and S2 are closed, the ammeter shows 0.45 A.

9. (Xiangyang High School Entrance Examination) The I-U images of resistors R1 and R2 are as shown in the figure. When the voltage on R2 is 1.5 V, the resistance of R2 is 10Ω; if they are connected in parallel to a power supply with a voltage of 2.5 V, the main circuit current is 0.7 A.

10. In the circuit as shown in the figure, the power supply voltage is constant 6 V, R=10 Ω, when the switch S is closed, the voltmeter indicates 2 V. Which of the following is correct (B)

A. The voltage across resistor R is 2 V

B. The ammeter shows 0.4 A

C. The resistance of the small light bulb is 20 Ω

D. The current through resistor R is 0.6 A

11. As shown in the figure is the schematic diagram of the gas alcohol concentration tester, which is used to test whether the driver is drunk and driving on site. The power supply voltage remains unchanged, R is a fixed-value resistor, and R' is a tin dioxide semiconductor alcohol gas sensor, and its resistance decreases as the alcohol concentration of the gas increases. If the voltage indication number in a certain test is large, it means (A)

A. The alcohol concentration of the gas is larger and the resistance value of R' is smaller.

B. The alcohol concentration of the gas is larger, and the resistance value of R' is larger.

C. The alcohol concentration of the gas is small, and the resistance value of R' is small.

D. The alcohol concentration of the gas is small and the resistance value of R' is large.

12. (Changzhou High School Entrance Examination) How to detect changes in plant water content from the outside? Scientists use hygroscopic resistors Rx made of strip graphene attached to the leaves. When the plant water content becomes lower, Rx becomes smaller, and the electrical value becomes smaller; The water content of the plant becomes higher, the Rx becomes larger, and the electric meter becomes larger. The power supply voltage is constant, R0 is a fixed value resistor, the following circuit diagram meets the requirements (C)

13. Places A and B are 40 km apart. Two transmission lines are erected along a straight line between places A and B. It is known that the resistance of the transmission lines used is 0.2 Ω per kilometer. It is found that a short circuit occurred somewhere in the transmission line. In order to determine the location of the short circuit, the maintenance personnel used a voltmeter, ammeter, fixed value resistor R0 and power supply to connect the circuit as shown in the figure for measurement. The reading on the voltmeter is 3.0 V and the reading on the ammeter is 0.5 A. Then the distance between the short circuit position and ground A is (B)

A.7.5 km B.15 km C.25 km D.30 km

Ohm's Law PPT, Part 3: Expanding, exploring and breaking through

16. (Lanzhou High School Entrance Examination) As shown in Figure A, the resistance of resistor R1 is 20 Ω, and the sliding rheostat R2 is marked with "50 Ω 2 A". When the sliding plate P of the sliding rheostat moves to end a, it is closed Switch S, the ammeter shows 0.3 A.

(1) Find the power supply voltage U;

(2) If a voltmeter is connected in parallel to both ends of the circuit (A and B), (B and C) or a certain part of the circuit (A and C), adjust the slider P of the sliding rheostat R2 so that the voltage The pointer of the meter points to the position shown in Figure B. Please indicate all possible connection positions of the voltmeter, and find the corresponding resistance value of the sliding rheostat R2.

Solution: (1) When the sliding plate P of the sliding varistor moves to terminal a, the resistance of the sliding varistor connected to the circuit is 0, and there is only R1 in the circuit. After closing the switch S, the ammeter A reads 0.3 A, that is, through R1 The current I1=0.3 A, according to Ohm's law, the voltage across R1 (ie, the power supply voltage)

U=I1R1=0.3 A×20 Ω=6 V

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