Question

method? RAPPING UP Kirchhoff s Rules necessary to analyze a circuit? Q13: Under what conditions are Q14: Do you think that the resistance of a voltage probe is large or small? Why? Q15: Do you think that the resistance of a current probe is large or small? Why? Q16: Can you think of a mechanical analogy to resistance? Explain your analogy. LEASE CLEAN UP YOUR AREA AND STRAIGHTEN YOUR CHAIRS, So 1 STATION IS READY FOR THE NEXTSTUDENTSTO US E IT.

Answer 1

Q13) Conditions necessary to analyse a circuit are as follows:

• Kirchhoff’s first rule—the junction rule. The sum of all currents entering a junction must equal the sum of all currents leaving the junction.
• Kirchhoff’s second rule—the loop rule. The algebraic sum of changes in potential around any closed circuit path (loop) must be zero.

Kirchhoff’s First Rule

Kirchhoff’s first rule (the junction rule) is an application of the conservation of charge to a junction; Current is the flow of charge, and charge is conserved; thus, whatever charge flows into the junction must flow out. Kirchhoff’s first rule requires that I₁ = I₂ + I₃ (see figure). Equations like this can and will be used to analyze circuits and to solve circuit problems.

Kirchhoff’s Second Rule

Kirchhoff’s second rule (the loop rule) is an application of conservation of energy. The loop rule is stated in terms of potential, V, rather than potential energy, but the two are related since PE_elec = qV. Recall thatemf is the potential difference of a source when no current is flowing. In a closed loop, whatever energy is supplied by emf must be transferred into other forms by devices in the loop, since there are no other ways in which energy can be transferred into or out of the circuit. Kirchhoff’s second rule requires emf − Ir − IR₁ − IR₂ = 0. Rearranged, this is emf = Ir + IR₁ + IR₂ = 0, which means the emf equals the sum of the IR (voltage) drops in the loop.

Q13)

• The probe itself usually has a low resistance, unless it contains a compensated divider (as is common for oscilloscopes), in which case it would have a very high resistance.
• The meter/oscilloscope itself has a high resistance.

Q14)

• Current probes are designed to offer a convenient way of measuring current and since the measurement is intended for low current levels, the voltage drop across this impedance is generally low and should have a minimal effect on the measurement.
• Current measurements using an oscilloscope generally use a current probe. It works the same as an electrician’s clamp-on ammeter, where heavy-duty jaws clamp around the conductor in which the current flow is to be measured.

Q14)

• Try using the analogy of water. In a water hose the force would be measured in PSI instead of Volts. The flow rate would be measured in GPM instead of Amperes. The resistance to the flow of water of the hose would be measured in inches of water column instead of Ohms.
• For a given PSI there will be more GPM in a larger diameter or shorter hose than in a smaller diameter or longer hose. This is akin to the resistance property of a length of wire. In a wire you are pushing free electrons. The more free electrons in a conductor, the lower its resistance to flow (Amperes) for a given force (Volts). Some of the ways in which you can decrease a conductors resistance are by making its cross section larger or using a shorter length.