A junior high school physics question, junior high school physics question?

The smaller the cross-sectional area of the wire, the greater the current. After the load limit of the wire is over, it will heat up or even fuse, and generally 1 square copper wire is allowed to pass a maximum of 6A current.

The smaller the cross-sectional area of the wire, the greater the current. The whole circuit is connected in parallel, but just look at the resistance and wires of the electrical appliances are connected in series, and according to the square of Q=i, the current is constant, the greater the r, the greater the electric heat, so choose C

When using the smell of rubber, touch the power cord with your hand and find that it is very hot, indicating that the heat generated on the power line is a lot, the wire is about to be burned out, at this time, the resistance of the wire relative to the electrical appliance, can not be ignored, the wire and the electrical appliance are in series, the thinner the wire, the greater the resistance, the total voltage is unchanged, but the voltage on the wire is larger, so the loss on the wire is also larger, and the heat generated is more.

q = i·i·r·t (Joule's law) (the square of i is not easy to beat, so hit two).

From the expression, we can know that the larger r is, the larger q is, and the thinner the wire, the greater the resistance, so the greater the electric heat.

Because the power of the rice cooker is 800W, and the normal household voltage is 220V, the resistance obtained by dividing the resistance by R=U2 P is too high, and the current of i=p u is high, and the use of thinner wires, as soon as the resistance is high, it will fuse, and the rubber outside will burn up! ~，

This is because the wire is too thin to withstand the heat it generates, and it has a burnt smell of rubber.

The thinner the wire, the greater the resistance and the more Joule heat.

In fact, the resistance of the wire is very small compared to the resistance of the rice cooker heating device, and when the resistance of the wire increases, it has little effect on the current.

And Joule heating = i 2rt, r increases, and q of course becomes larger.

Because the maximum current is beyond the range that the ammeter can tolerate (0, in order not to damage the instrument, the maximum can only be adjusted.

Because the maximum current that can be generated exceeds the maximum current of the ammeter, it is not safe, and the maximum value of the ammeter can only be the maximum value of the ammeter in order to ensure safety.

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I kind of want to laugh, the maximum support of the ammeter is because you can't choose the range of 3A, and then calculate the interval of the ratio through the extreme value.

First, before the installation of high-strength bolts, it is necessary to carry out anti-slip friction test and tensile strength test of friction surface, and only after the test results are qualified, high-strength bolts can be installed; second, the vertical support, connecting plate, anchor bolt mounting frame, column, beam, etc. are all steel frames; Thirdly, because there are a variety of structures in the platform escalator, such as enclosure structure, escalator, platform beam, etc., the platform escalator must be effectively protected; Fourth, before hoisting the steel frame, for the foundation of the boiler room, the civil engineering professional will carry out the handover of relevant tasks to the boiler installation professional, after the foundation of the boiler room is qualified, the steel frame can be hoisted, after the installation of the first layer of steel frame structure, the civil engineering professional and the installation professional carry out the handover of the task, in order to ensure the grouting quality of the foot bolts, the handover of related tasks should be continuously carried out to ensure that the quality of all links of the steel frame hoisting meets the requirements.