In the second year of junior high school, physics and electricity calculation questions must have an

The voltage at both ends of a certain resistor is 10V

The passing current is 5A

Find its resistance. Solution:

i=u r,r=u i=10 5=2 ( ) is the ohm symbol will not be hit) Answer: .Everything is changing, and you don't have to worry about anything after learning well. This is an example, and the endless variety of questions can never be finished. It seems simple.

Tell your sister.

Question: The power supply, ammeter, fixed value resistance R1, and sliding rheostat R2 are connected in series, and the voltmeter measures the resistance voltage, when U=3V, I=, find R=?

Solution: r=5

Solution: u=3v, i=

According to Ohm's law i = u r deformation is obtained: r = u i = 3v

Answer: The resistance is equal to 5

Figure 16 is the working principle diagram of a brand of household rice cooker, and the resistance value of R2 is known to be 44; When the s1 is closed and closed separately, the rice cooker is in a state of heat preservation, and the heat preservation power at this time is 40W

1) What is the R1 resistance?

2) Close the switch S1 S2 at the same time, how much electricity does the rice cooker consume when it works for 1min?

1) Resistance value of R1: R1 U2 P insulation (220V)2 40W 1210

2) When the switch S1 S2 is closed at the same time, the two resistors are connected in parallel, and the power consumed by working 1minr1: W1 P insulation t 40W 60S 103JR2 power consumed: W2 U2 R2 T (220V)2 44 60S 6

6×104j

The electrical energy consumed by the circuit: w w1 w2

Example 3 In the circuit shown in Figure 15-1, the power supply voltage U=6V and remains unchanged, the resistance R=5, and the resistance range of the sliding rheostat is 0-10 In the process of moving the sliding blade of the sliding rheostat from the left end to the right end, find:

1) After the switch is closed, what is the indication range of the ammeter and voltmeter?

2) What is the maximum amount of electrical energy consumed by the resistor R within 25s when the circuit is turned on?

Analysis: When the slide p moves to the left or right, the current in the circuit becomes larger or smaller, respectively. Obviously, when the slider slides to the left end, the current in the circuit is maximum, and the voltage at both ends of the resistor r is the largest and equal to the supply voltage; When the slide slides to the right end, the current in the circuit is minimal

Full solution: When the slide slides to the left end, r slips 1=0, a=, ur=6v When the slide slides to the right end, r slips 2=10 , a=,u'r=i'r= For resistors r, when the sliding rheostat slide moves to the left end, the current in the circuit is maximum, thus consuming the most electrical energy in an equal time

w=i2rt=(

Therefore, in this problem, (1) the indication range of the ammeter is 6V-2V; (2) The maximum electrical work is.

R1 = 3 ohms, R2 = 5 ohms, in parallel on a power supply with a voltage of 6V, turn on for 3 min to find: (1) Q1 = ?

2）q2=？

3) r total = ?

Solution: (1) t=3min=180s

Q1=i rt=u rt=(6v) 3 ohms·180s=2160j(2)q2=i rt=u rt=(6v) 5 ohms·180s=1296j

3) It is in parallel.

1 r total = 1 r1 + 1 r2

r total = r1r2 r1 + r2 = (3 euros + 5 euros) 3 5 = (8 15) euros.

The two resistors of A and B are connected in series in the circuit, the voltage at both ends of A is 3V, and the resistance of B is 5 ohms.

One resistor is 5 ohms, and the other resistor is 10 ohms, what is the total resistance after series connection?

A: Total resistance = 5 ohms + 10 ohms = 15 ohms.

The current and voltage of the series circuit have the following rules: (such as: R1, R2 in series).

Current: i=i1=i2 (the current is equal everywhere in the series circuit).

Voltage: U=U1+U2 (the total voltage is equal to the sum of the voltages everywhere).

Resistance: r=r1+r2 (total resistance is equal to the sum of each resistance) If n resistors with the same resistance value are connected in series, then there is r total = nr

2. The current and voltage of parallel circuit have the following rules: (such as: R1, R2 in parallel).

Current: i=i1+i2 (the trunk current is equal to the sum of the currents of each branch).

Voltage: u=u1=u2 (the main circuit voltage is equal to the voltage of each branch).

Resistance: (The reciprocal of the total resistance is equal to the reciprocal sum of the various parallel resistors) or .

If n resistors with the same resistance value are connected in parallel, then there is r total = r

Note: The total resistance of a parallel circuit is smaller than that of any one of the branches.

The formula for calculating electrical work is: w=uit (unit w joule (j); u volts (v); i Ann (a); t seconds).

5. When using w=uit to calculate electrical work, pay attention to the following: w, u, i and t in the formula are in the same circuit section; The unit of calculation should be unified; Any three quantities known can be found to be a fourth quantity.

6. The following formula can also be used to calculate electrical work: w=i2rt; w=pt；w=uq (q is the amount of electricity); 7.The definition of electrical power is p=ui

When the circuit is a pure resistive circuit (that is, most of the electrical energy consumed by the appliance is used to generate heat, such as a heating wire or incandescent lamp), each derivation can be used p=u i=u 2 r=i 2r

If it's not pure (e.g. hair dryer), if you ask about heat production, use p=u 2 r=i 2r

Q: The total power is p=ui

In fact, the third year of junior high school electricity is mainly electrical work and electric power.

The definition of electrical power is p=ui

When the circuit is a pure resistive circuit (that is, most of the electrical energy consumed by the appliance is used to generate heat, such as a heating wire or incandescent lamp), each derivation can be used p=u i=u 2 r=i 2r

If it's not pure (e.g. hair dryer), if you ask about heat production, use p=u 2 r=i 2r

Q: The total power is p=ui

This is how the electrical work formula is used.

Hehe, I know that you must not have listened carefully to the teacher's lecture when you asked the question, and if you can ask this question, it means that you like physics very much and want to learn it well. Then I'll tell you:

The physical formula is more of an electrical part, because there are two kinds of circuits: series and parallel. The current of the series circuit is equal and the voltage of the parallel circuit is equal, so the formula must not be used incorrectly.

The formula in a series circuit: i=i1=i2 r=r1+r2 u=u1+u2

The formula in a parallel circuit: i=i1+i2 u=u1+u2 1 r=1 r1 +1 r2

Okay, that's all there is to it. Thank you for enjoying learning physics.