April 26/28
Physics
Table of Contents#. Date Title-Page – Page Number29.April 14/15 Electrostatics30.April 18/19 Electric Field31.April 20/21 Electrostatics Problems32.April 22/25 Circuits33.April 26/28 Measuring Electricity
1
Homework #4
In:
Label each diagram as series or parallel:
Objective: To understand Ohm’s
law and measure:• Simple• Series• Parallel circuits
Success criteria:
Calculate and measure current, voltage and resistance.
Amount of charge passing by every second:
CurrentI=ΔQ Δt
Measured in Amperes1 Ampere= 1 Coulomb
second
If a current of 45.0 mA exists in a metal wire, how much charge goes through in 20 minutes?
How many electrons flow past a given cross section of the wire in 10.0 min?
Sketch the direction of the current and the direction of the electrons’ motion.
Energy of each charge
Electric potential
V measured in Volts
Energy
charge
• Voltage is like a pinball machine pushing the electrons out of the source into the circuit
Resistance to flow of electrons
Resistance
Measured in Ohms
Ω
• Resistance slows down the flow of electrons– Voltage used up – Light emitted– Heat emitted
• How do you think the current would change if you increase the resistance in a circuit?
• How do you think the current would change in a circuit if you increase the voltage into a circuit?
Ohm’s Law
Georg Simon Ohm
• German physicist
• The relationship between current and voltage
• 1827
Ohm’s Law
V=IR
A lightbulb has a resistance of 240 Ω when operating at a voltage of 120 V. What is the current in the bulb?
A toaster has a resistance of 10 kΩ. How much current flows through it at a voltage of 120V?
What is the resistance of a hair dryer if it runs at 120V with a current of 1 A?
What is the current of a lightning bolt that has a voltage of 10 million volts through air with a resistance of 2 KΩ?
Lab: Using a Multimeter
Purpose: to measure circuits.
How to measure resistance voltage and current
Reading a Resistor
Measuring Voltage
• -Direct measurement of the push
• -Connect directly to the battery (or circuit if you want to measure change in voltage)
Measuring Resistance
-Connect leads to resistor
-Outside of a circuit
Measuring Current
• Must be a circuit
• Circuit must include the meter
Out:
A hairdryer takes 1 amp of current at 120 V. What is its resistance?