Ohm’s Law and Power
THE ELECTRIC CIRCUIT
• A practical electric circuit has at least four parts: (1) a source of electromotive force, (2)
conductors, (3) a load, and (4) a means of control (Fig. 3-1). The emf is the battery, the
conductors are wires that connect the various parts of the circuit and conduct the
current, the GEUT0213 – Engineering Utilities-1 15 resistor is the load, and the switch is
the control device. The most common sources of emf are batteries and generators.
Conductors are wires which offer low resistance to a current. The load resistor
represents a device that uses electric energy, such as a lamp, bell, toaster, radio, or a
motor. Control devices might be switches, variable resistances, fuses, circuit breakers, or
relays.
• A complete or closed circuit (Fig. 3-1) is an unbroken path for current from the emf,
through aload, and back to the source. A circuit is called incomplete or open (Fig. 3-
2a) if a break in thecircuit does not provide a complete path for current.
, • To protect a circuit, a fuse is placed directly into the circuit (Fig. 3-2b). A fuse will open the
circuit whenever a dangerously large current starts to flow. A fuse will permit currents smaller
than the fuse value to flow but will melt and therefore break or open the circuit if a larger
current flows, a dangerously large current will flow when a “short circuit” occurs. A short
circuit is usually caused by an accidental connection between two points in a circuit which offers
very little resistance (Fig. 3-2b).
• A ground symbol is often used to show that a number of wires are connected to a
common point in a circuit. For example, in Fig. 3-3a, conductors are shown making a
complete circuit, while in Fig. 3-3b, the same circuit is shown with two ground
symbols at G1 and G2. Since theground symbol means that the two points are
connected to a common point, electrically the two circuits (Fig. 3-3a and b) are
exactly the same.
THE ELECTRIC CIRCUIT
• A practical electric circuit has at least four parts: (1) a source of electromotive force, (2)
conductors, (3) a load, and (4) a means of control (Fig. 3-1). The emf is the battery, the
conductors are wires that connect the various parts of the circuit and conduct the
current, the GEUT0213 – Engineering Utilities-1 15 resistor is the load, and the switch is
the control device. The most common sources of emf are batteries and generators.
Conductors are wires which offer low resistance to a current. The load resistor
represents a device that uses electric energy, such as a lamp, bell, toaster, radio, or a
motor. Control devices might be switches, variable resistances, fuses, circuit breakers, or
relays.
• A complete or closed circuit (Fig. 3-1) is an unbroken path for current from the emf,
through aload, and back to the source. A circuit is called incomplete or open (Fig. 3-
2a) if a break in thecircuit does not provide a complete path for current.
, • To protect a circuit, a fuse is placed directly into the circuit (Fig. 3-2b). A fuse will open the
circuit whenever a dangerously large current starts to flow. A fuse will permit currents smaller
than the fuse value to flow but will melt and therefore break or open the circuit if a larger
current flows, a dangerously large current will flow when a “short circuit” occurs. A short
circuit is usually caused by an accidental connection between two points in a circuit which offers
very little resistance (Fig. 3-2b).
• A ground symbol is often used to show that a number of wires are connected to a
common point in a circuit. For example, in Fig. 3-3a, conductors are shown making a
complete circuit, while in Fig. 3-3b, the same circuit is shown with two ground
symbols at G1 and G2. Since theground symbol means that the two points are
connected to a common point, electrically the two circuits (Fig. 3-3a and b) are
exactly the same.
