Example 7.1.1:Junctions,branches and loops In the circuit shown in Figure 7.1.1(a),there are two junctions,A and B,on either side of light bulb 1.There are three branches:branch 1 goes from A to B through the battery, branch 2 goes from A to B through light bulb 1,and branch 3 goes from A to B through light bulb 2.There are three closed loops.We shall describe the loops by arbitrarily starting at junction A.Loop 1 consists of branches 1 and 2;it starts at junction A,passes through the battery to junction B,and then from junction B back to junction A through light bulb 1.Loop 2 consists of branches 2 and 3;it starts at junction A,passes through light bulb I to junction B,then continues through light bulb 2 back to junction A.Loop 3 consists of branches 1 and 3;it stars at junction A,passes through the battery to junction B,then continues through bulb 2 back to junction A.The circuit shown in Figure 7.1.1(b) has no junctions,one branch and one closed loop. Elements are said to be in parallel when they are connected across the same potential difference.Both light bulbs in Figure 7.1.1(a)are connected across the battery.Generally, loads are connected in parallel across the power supply.On the other hand,when the elements are connected one after another in a branch,the same current passes through each element,and the elements are in series (see Figure 7.1.1b). There are pictorial diagrams that show wires and components roughly as they appear,and schematic diagrams that use conventional symbols,somewhat like road maps.Some frequently used symbols are shown in the Table below. Often there is a switch in series;when the switch is open the load is disconnected;when the switch is closed,the load is connected. Electromotive Source Seat of emf Resistor Switch One can have closed circuits,through which current flows,or open circuits in which there are no currents.Usually by accident,wires may touch,causing a short circuit.Most of the current flows through the short,very little will flow through the load.This may burn out a piece of electrical equipment such as a transformer.To prevent damage,a fuse or circuit breaker is put in series.When there is a short the fuse blows,or the breaker opens. 7-47-4 Example 7.1.1: Junctions, branches and loops In the circuit shown in Figure 7.1.1(a), there are two junctions, A and B, on either side of light bulb 1. There are three branches: branch 1 goes from A to B through the battery, branch 2 goes from A to B through light bulb 1, and branch 3 goes from A to B through light bulb 2. There are three closed loops. We shall describe the loops by arbitrarily starting at junction A. Loop 1 consists of branches 1 and 2; it starts at junction A, passes through the battery to junction B, and then from junction B back to junction A through light bulb 1. Loop 2 consists of branches 2 and 3; it starts at junction A, passes through light bulb 1 to junction B, then continues through light bulb 2 back to junction A. Loop 3 consists of branches 1 and 3; it stars at junction A, passes through the battery to junction B, then continues through bulb 2 back to junction A. The circuit shown in Figure 7.1.1(b) has no junctions, one branch and one closed loop. Elements are said to be in parallel when they are connected across the same potential difference. Both light bulbs in Figure 7.1.1(a) are connected across the battery. Generally, loads are connected in parallel across the power supply. On the other hand, when the elements are connected one after another in a branch, the same current passes through each element, and the elements are in series (see Figure 7.1.1b). There are pictorial diagrams that show wires and components roughly as they appear, and schematic diagrams that use conventional symbols, somewhat like road maps. Some frequently used symbols are shown in the Table below. Often there is a switch in series; when the switch is open the load is disconnected; when the switch is closed, the load is connected. Electromotive Source Seat of emf Resistor Switch One can have closed circuits, through which current flows, or open circuits in which there are no currents. Usually by accident, wires may touch, causing a short circuit. Most of the current flows through the short, very little will flow through the load. This may burn out a piece of electrical equipment such as a transformer. To prevent damage, a fuse or circuit breaker is put in series. When there is a short the fuse blows, or the breaker opens