# Which wire can carry more current?

## Understand physics 4, textbook

54 3  Workbook, pages 30–31 54.1 Scorched plugs and sockets 1. How can cables overheat? The glowing wire (Fig. 54.2) Set up the circuit as shown in Fig. 54.2. Put an alligator clip with a pin in each of the sockets A and B. Clamp a piece of resistance wire (Ø = 0.2 mm) approx. 10 cm long between the two. You apply 12V direct current from the student power supply to the circuit. Close the switch. Bridge the glowing lamp by plugging a cable into sockets C and D (short circuit). What will happen to the resistance wire? A short circuit reduces the electrical resistance in the circuit and the wire begins to glow (V1). Excessive currents can lead to overheating of cables (risk of fire). We therefore need line protection. M A short circuit or overload (too many electrical devices in operation) will reduce the resistance in the circuit. As a result, the amperage increases sharply and the cables overheat. Insulations become soft or melt! 2. Which devices protect against overheating and overload? The fuse melts (Fig. 54.3) Take over the circuit from V1. After the switch, replace a straight piece of line with a "fuse model". Clamp a piece of safety wire (Ø = 0.2mm) between his alligator clips. Apply 12V DC to the circuit again, close the switch and create a short circuit. How is the circuit now protected? In the event of a short circuit, the current increases rapidly. The fuse wire of a fuse melts, interrupts the circuit and the lines do not heat up. Colored identification plates show the maximum current ratings of the fuses. Electromagnetic circuit breakers are mostly used for line protection. M With the fuse, a very thin wire melts if the current is too high. In the case of the miniature circuit-breaker, an electromagnet or a bimetal interrupts the circuit. V1 V2 Dangers of electric current 12V = resistance wire 10V / 0.05A C D A B Safety wire short circuit 54.3 The fuse melts. 54.4 Miniature circuit breaker for several circuits in the switch box 54.5 Electrical device with insufficient protection 54.6 Symbols: all-insulated or device tested by the Austrian Association of the Electrical Industry 54.2 The glowing line 12V = resistance wire 10V / 0.05A CDAB short circuit Worksheets cp84uz For test purposes only - property of the publisher öbv