Lab 18: What Is the Relationship Between Pressure Difference and Flow Rate?

Lab 18: What is the relationship between Pressure Difference and Flow Rate?

Investigation 1: Deriving the Relationship with a resistor

1 to 6 cells

Use Excel to plot data to find the relationship between DV and I.

Investigation 2: Checking the relationship with a bulb

Use Excel to plot data to find the relationship between V and I.

Discussion Questions

1. In terms of experimental data how is resistance defined and what are its units?

2. Look back at the lab you did to discover Ohm's Law.

a) Sketch a graph of pressure difference vs. flow rate that describes the behavior of a third resistor that has a much smaller resistance than the ones used in the lab activity.

b) How would the flow rate through this resistor change as the pressure difference decreases?

3. Assume that resistor A has 10 times the resistance of resistor B. What would a graph of resistance vs. current look like for these two resistors (sketch them on the same axes)? What about a graph of resistance vs. voltage? Justify your answers.

4. While cooking dinner, the school's dining hall oven uses a 220 Volt line and draws 10 A of current when heated to its maximum temperature. What is the resistance of the oven when it is fully heated?

5. A circuit containing three parallel branches. The first two branches have identical resistance, but the third branch’s resistance is half the resistance of the first two. The currents in each of the first two parallel branches are each 3 amps.

a) What is the current in the last branch of the circuit?

b) If the battery has a voltage of 12 Volts, what is the resistance in the first two parallel branches?

c) What is the resistance in the third branch?

d) What is the total resistance of the circuit?

6. Before coming to school Gene runs his 18 Ω toaster, 11 Ω electric frying pan, 14 Ω electric coffee maker and a 5 Ω electric toothbrush. The four are connected in parallel across a 120 V line.

a) What is the current through each appliance?

b) If a household circuit could carry a maximum current of 15 A (the fuse in the circuit break is a 15 A fuse), would Gene be able to run all of these appliances at the same time?

7. Your house is rated for 150 Amps of service and is protected by a 150 Amp circuit breaker. Each room in your house is wired in parallel. The kitchen has an 18 ohm toaster, a 14 ohm electric coffee maker, an 11 ohm frying pan, a 7 ohm stove, a 8 ohm refrigerator. You living room has an 11 ohm TV, and a 5 ohm lamp. Your bedroom has two 5 ohm lamps and a 8 ohm stereo. When all of your appliances are running at the same time will your 150 Amp circuit breaker break?

8. Old-fashioned holiday lights were connected in series across a 120 V household line. If a string of these lights consists of 12 bulbs, what is the potential difference across each bulb? If the bulbs were connected in parallel, what would be the potential difference across each bulb?

9. Examine the graph of electric pressure difference vs. flow rate on the right.

a) Is this resistor Ohmic or non-Ohmic?

b) What is the resistance of the object from which this data

was collected?

10. A 9 volt battery is connected to a 6W resistor. What will the flow rate through the resistor be?