![](data:image/svg+xml;utf8,<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 0 72 71" width="72"></svg>)
To connect a small bulb marked with "6v-30w" to 18V power supply for normal lighting, what is the resistance in series? What is the electric power of the resistance?
6V30W
So the current is 5A and the resistance is 1.2 ohm
In normal operation, the current should be constant
So a 2.4 ohm resistor needs to be connected in series
Square of resistance power 2.4 * 5
60W
A 500 W electric heater was used to heat water for 2 min. the water temperature increased from 90 ℃ to 95 ℃ and stopped heating for 1 min. the water temperature decreased by 1 ℃ to get m water
RELATED INFORMATIONS
- 1. How long does it take to make 80kg water from 20 ℃ to 55 ℃ with the electric heater of "220V 1.8kw" fast
- 2. It is known that R1 = 10 Ω, R2 = 20 Ω. If they are connected in series and connected to a 6V power supply, the power consumption of resistor R1 and R2 per minute is If they are connected to the same power supply, the work done by the current to r1r2 per minute is
- 3. The electromotive force of the power supply is 2V and the internal resistance is 0.1 ohm. When the external circuit is open, the current and terminal voltage in the circuit are
- 4. Generally speaking, when the load resistance decreases, the load increases, and the power output power increases (×), how to explain
- 5. A small electric bell with a resistance of 10 ohm is connected in series with a fixed resistance of 20 ohm and connected to a 6V power supply. If the small electric bell just works normally, what is the voltage at both ends of the electric bell?
- 6. There are three resistors, R1 = 8 ohm, R2 = 12 ohm, R3 = 20 ohm. Connect them in series with a 10 volt power supply. What is the voltage at both ends of the three resistors?
- 7. If resistance R1 is connected to a circuit, the power consumed is P1; if another resistance R2 is connected to the same circuit in series, the power consumed by R2 is P2. If P1: P2 = 4:1, R1 "select" greater than "," less than ", or" equal to "R2
- 8. Connect two fixed value resistors in series to both ends of the power supply with voltage of u, the power consumed by R1 is P1, and the power consumed by R2 is 3P1 A. The ratio of voltage between R1 and R2 in series is 3:1b. The power consumed by R1 in parallel is 16p1c. The ratio of current through R1 and R2 in parallel is 1:3d. The total power consumed by two resistors in parallel is 163p1
- 9. If the two constant resistors R1 and R2 are connected to the power supply in some way, the power consumed by R1 is 9W, If the two resistors are connected to the power supply in another way, the power consumed by R1 is 16W, and the current passing through R2 is 4a. If the power supply voltage remains unchanged, what is the power supply voltage and the resistance of r1r2
- 10. Two fixed value resistors R1 and R2 are connected in parallel and connected to the circuit. Their electric power is P1 and P2 respectively, and the total power is p. try to prove that P = P1 + P2
- 11. One day, Xiao Ming found that an old incandescent lamp marked "220 V & nbsp; & nbsp; 40 W" was dim. He ran to the corridor to observe the electric energy meter, and measured the electric power of 1200 W with his watch. (1) "it can't be the electric power of the incandescent lamp!" Xiaoming checked that the reading and calculation were correct, and the watt hour meter and watch were accurate. With the help of his father, the voltage at both ends of the incandescent lamp was measured to be 220 v. please analyze the cause of this error______ (2) after analyzing the cause and correcting the error, Xiao Ming measured again that the electric power of this lamp is 36W. The reason why the actual power of the incandescent lamp is lower than the rated power is that______ ．
- 12. What is the heating rate of the electric heating wire in the hair dryer
- 13. Is the motor and resistance wire in the hair dryer in series or in parallel
- 14. If you want to change the hair dryer to make the temperature of hot air higher, you should connect a resistance wire to the original resistance wire
- 15. What kind of energy does a hair dryer turn into when it blows cold air
- 16. What is the electric power of the bulb marked with "3V 3W" when passing 0.2A current?
- 17. A lamp is connected to the home circuit. The current passing through is 0.2A. How about the electric power of the lamp?
- 18. Do you need to adjust the ohm to zero after measuring the resistance of 4 ohm and 5 ohm with the ohm gear of the multimeter Do you need to adjust the ohm to zero after measuring the resistance of 4 ohm and 5 ohm respectively with the ohm gear of the multimeter
- 19. Physics problems about Joule's law The unit length of a wire is 0.01 Ω / m, which is now used for household circuit power supply. The resistance of the electric furnace at 100m is about 48 Ω. How much heat does the wire generate per minute? If the electric furnace is short circuited, how much heat does the wire generate per second?
- 20. What about Joule Lenz's law? 1: Is Joule Lenz's law a person? 2: Joule Lenz law I read in a book that the heat generated by a circuit is directly proportional to the square of the current intensity, the resistance, and the time of the current flowing. Later, I thought, it's not quite right. First, in a circuit, of course, the larger the resistance is, the greater the heat generated, the smaller the line resistance is, the smaller the power transmission is, and the smaller the loss is. Of course, the smaller the heat generated, but on the other hand, for example, the electric furnace, The smaller the resistance of the electric furnace wire, the greater the power, and the greater the heat generated. How can it be reversed?