Chapter 17 Current and Resistance 1. Electric current 2. Drift speed 3. Current and voltage...

Chapter 17

Current and Resistance1. Electric current2. Drift speed3. Current and voltage measurement4. Ohm’s law5. Resistivity6. Superconductivity7. Electric energy and power

Electric Current What is an electric current? How do I calculate current? What are the SI units? What is the direction of current in

a circuit? What is conventional current?

Current and Drift Speed Current defined in

terms of charge carrier and drift speed

Isolated conductor Conductor with

electric field Drift speed and

circuits

Example

1. The battery pack of a pocket calculator has a voltage of 3.0 V and delivers a current of 0.17 mA. In one hour of operation,

a) How much charge flows in the circuit?

b) How much energy does the battery deliver to the calculator circuit?

Meters in a Circuit

What is an ammeter? How do I connect it in a circuit? What is a voltmeter? How do I connect it in a circuit?

Resistance What is a resistor? What is the relationship between

voltage and current in a circuit? What is electrical resistance? What the SI units of resistance? What is Ohm’s law?

Georg Simon Ohm 1787 – 1854 Formulated the

concept of resistance

Discovered the proportionality between current and voltages

Ohm’s Law Statement of

ohm’s law What is an Ohmic

device? What is non-

Ohmic device? Examples

Example1. A filament in a light bulb is

resistor in the form of a thin wire. The wire becomes hot enough to emit light because of the current in it. A flashlight uses two 1.5 V batteries to provide a current of 0.40 A in the filament. Determine the resistance of the glowing filament.

Resistance & Resistivity What is resistivity? Resistivity of metals? See table 17.1 Resistance and Temperature

Example1. The heating element in an electric

stove contains a wire of 1.1m and cross-sectional area 3.1x10-6 m2 through which electric charge flows. The wire becomes hot in response to the flowing charge. The resistivity of the material is 6.8x10-3 °C-1 at 320 °C. Determine the resistance of the heater wire at an operating temperature of 420 °C.

Superconductors What are

superconductors? Why

superconductors?

Energy Transfer in the Circuit What is

grounding? Energy

considerations

Electrical Energy and Power What is power? How do I calculate it? What are the SI units? What is kilowatt-hour? Conversion factor

Example

1. In the flashlight the current is 0.40A and the voltage is 3.0 V. Find

a) The power delivered to the bulbb) The electrical energy dissipated in

the bulb in 5.5 minutes of operation.

Electrical Activity in the Heart

Normal

Implanted Cardioverter Defibrillator (ICD)

Devices that can monitor, record and logically process heart signals

Then supply different corrective signals to hearts that are not beating correctly