Physics Lab

Leslie WatkinsGuilhem Ribeill

NCSO Coaches’ Clinic 2008

Overview/ Rules

• A team of up to 2 students will compete in lab activities in the areas of work, energy, and power.

Overview/ Rules

• A team of up to 2 students will compete in lab activities in the areas of work, energy, and power.

• Approximate time: 50 minutes

Overview/ Rules

• A team of up to 2 students will compete in lab activities in the areas of work, energy, and power.

• Approximate time: 50 minutes• Students may bring and use any non-

programmable calculator. No other resource materials or electronic devices may be used unless provided by the event supervisor.

Overview/ Rules

• The competition will consist of experimental tasks and questions related to energy and alternative energy.

Skills

• Students are expected to know concepts, definitions and basic equations for work, kinetic energy, gravitational potential energy, spring potential energy, power, electric energy stored in capacitors, electrical power, heat produced in electrical resistance, work done by fluids, fluid power, rotational work, rotational power, efficiency of conversions based on work, energy, and power.

Skills

• Students are expected to know concepts, definitions and basic equations for work, kinetic energy, gravitational potential energy, spring potential energy, power, electric energy stored in capacitors, electrical power, heat produced in electrical resistance, work done by fluids, fluid power, rotational work, rotational power, efficiency of conversions based on work, energy, and power.

Skills

• Students are expected to know concepts, definitions and basic equations for work, kinetic energy, gravitational potential energy, spring potential energy, power, electric energy stored in capacitors, electrical power, heat produced in electrical resistance, work done by fluids, fluid power, rotational work, rotational power, efficiency of conversions based on work, energy, and power.

Skills

• Students are expected to know concepts, definitions and basic equations for work, kinetic energy, gravitational potential energy, spring potential energy, power, electric energy stored in capacitors, electrical power, heat produced in electrical resistance, work done by fluids, fluid power, rotational work, rotational power, efficiency of conversions based on work, energy, and power.

Skills

• Students are expected to know concepts, definitions and basic equations for work, kinetic energy, gravitational potential energy, spring potential energy, power, electric energy stored in capacitors, electrical power, heat produced in electrical resistance, work done by fluids, fluid power, rotational work, rotational power, efficiency of conversions based on work, energy, and power.

Skills

• Students are expected to know concepts, definitions and basic equations for work, kinetic energy, gravitational potential energy, spring potential energy, power, electric energy stored in capacitors, electrical power, heat produced in electrical resistance, work done by fluids, fluid power, rotational work, rotational power, efficiency of conversions based on work, energy, and power.

Skills

• Students are expected to know concepts, definitions and basic equations for work, kinetic energy, gravitational potential energy, spring potential energy, power, electric energy stored in capacitors, electrical power, heat produced in electrical resistance, work done by fluids, fluid power, rotational work, rotational power, efficiency of conversions based on work, energy, and power.

Skills

• Students are expected to know concepts, definitions and basic equations for work, kinetic energy, gravitational potential energy, spring potential energy, power, electric energy stored in capacitors, electrical power, heat produced in electrical resistance, work done by fluids, fluid power, rotational work, rotational power, efficiency of conversions based on work, energy, and power.

Skills

• Students are expected to know concepts, definitions and basic equations for work, kinetic energy, gravitational potential energy, spring potential energy, power, electric energy stored in capacitors, electrical power, heat produced in electrical resistance, work done by fluids, fluid power, rotational work, rotational power, efficiency of conversions based on work, energy, and power.

Skills

• Students are expected to know concepts, definitions and basic equations for work, kinetic energy, gravitational potential energy, spring potential energy, power, electric energy stored in capacitors, electrical power, heat produced in electrical resistance, work done by fluids, fluid power, rotational work, rotational power, efficiency of conversions based on work, energy, and power.

Skills

• Students are expected to know concepts, definitions and basic equations for work, kinetic energy, gravitational potential energy, spring potential energy, power, electric energy stored in capacitors, electrical power, heat produced in electrical resistance, work done by fluids, fluid power, rotational work, rotational power, efficiency of conversions based on work, energy, and power.

Skills

• Students are expected to know concepts, definitions and basic equations for work, kinetic energy, gravitational potential energy, spring potential energy, power, electric energy stored in capacitors, electrical power, heat produced in electrical resistance, work done by fluids, fluid power, rotational work, rotational power, efficiency of conversions based on work, energy, and power.

Skills

• Students are expected to know concepts, definitions and basic equations for work, kinetic energy, gravitational potential energy, spring potential energy, power, electric energy stored in capacitors, electrical power, heat produced in electrical resistance, work done by fluids, fluid power, rotational work, rotational power, efficiency of conversions based on work, energy, and power.

Skills

• Students are expected to know concepts, definitions and basic equations for work, kinetic energy, gravitational potential energy, spring potential energy, power, electric energy stored in capacitors, electrical power, heat produced in electrical resistance, work done by fluids, fluid power, rotational work, rotational power, efficiency of conversions based on work, energy, and power.

Skills

• Students are expected to know concepts, definitions and basic equations for work, kinetic energy, gravitational potential energy, spring potential energy, power, electric energy stored in capacitors, electrical power, heat produced in electrical resistance, work done by fluids, fluid power, rotational work, rotational power, efficiency of conversions based on work, energy, and power.

Skills

• Students are expected to know concepts, definitions and basic equations for work, kinetic energy, gravitational potential energy, spring potential energy, power, electric energy stored in capacitors, electrical power, heat produced in electrical resistance, work done by fluids, fluid power, rotational work, rotational power, efficiency of conversions based on work, energy, and power.

Skills

• Students are expected to know concepts, definitions and basic equations for work, kinetic energy, gravitational potential energy, spring potential energy, power, electric energy stored in capacitors, electrical power, heat produced in electrical resistance, work done by fluids, fluid power, rotational work, rotational power, efficiency of conversions based on work, energy, and power.

Summary of Equations

Skills

• All answers are to be provided in SI units (such as Watt, Joule, kilogram, meter, and second) with proper significant figures. The event supervisor will provide any equation beyond those the students are expected to know.

Skills

• All answers are to be provided in SI units (such as Watt, Joule, kilogram, meter, and second) with proper significant figures. The event supervisor will provide any equation beyond those the students are expected to know.

• Students may be asked to collect data using equipment that has been provided, set-up, and demonstrated by the supervisor.

Sample Stations• Electrical Energy to Mechanical Energy (Motors)• Electrical Energy to Electrical Energy (Transformers)• Solar Energy to Electric Energy (Photovoltaic Cells)• Gravitational Energy to Kinetic Energy• Rotational Energy to Gravitational Potential Energy• Pressure/ Volume Change to Kinetic and/or Gravitational

Potential Energy• Spring Energy to Kinetic and/or Gravitational Potential

Energy• Wind Energy to Electric Energy• Energy stored in Capacitor to Mechanical Energy• Efficiency of collisions (eg. Bouncing ball)

Problem-Solving Techniques

1) Identify/Visualize The Problem2) Determine Input Values3) Determine the Appropriate Equation4) Compute output5) Check solution

Visualizing the Problem

• Ask yourself: “what’s really going on here?”• It’s usually VERY important to draw the

problem!

Checking Your Answer

• Does my answer make sense? - if you find the mass of the earth to be 12

grams, you probably did something wrong!

• Units, units, units, units! - almost everything in physics has units – are

yours the right ones? If not, something might have gone wrong!

An example!

A photovoltaic cell with an area of 2 m2 is used to power a heater. The heater is a large 75 Ω resistor which draws one 2A of current. If the photovoltaic cell is 10% efficient, how much power is the solar cell receiving from the sun?

Solution1) Draw a picture!

2) Which equation is relevant? P = I2R for the resistor (heater)3) Compute: P = (2A)(75Ω) = 150 W produced by the cell4) If the cell is 10% efficient, then the sun must be producing 150W/0.1 = 1500 W of power

Example, Continued

Now supposed we’re asked to find how much energy the sun delivers to the earth’s surface per square meter per day.

Example, Continued

Now supposed we’re asked to find how much energy the sun delivers to the earth’s surface per square meter per day.

But we don’t have an explicit equation for this!

Example, Continued

Now supposed we’re asked to find how much energy the sun delivers to the earth’s surface per square meter per day.

But we don’t have an explicit equation for this!

Stay cool. We’ll use Dimensional Analysis

Example, Continued

Now supposed we’re asked to find how much energy the sun delivers to the earth’s surface per square meter per day.

But we don’t have an explicit equation for this!

Stay cool. We’ll use Dimensional Analysis

Dimensional Analysis? What’s that?

Dimensional Analysis?

Dimensional analysis is using the units as clues to figuring out the appropriate equation.

Since all physical quantities have units, by looking at the units of the input and output, we often figure out what to do without having to remember complicated equations

This can save a lot of time!

Dimensional Analysis!

The sun delivers 1500 W of power to a 2 m2 solar cell.Well, we want the energy per square meter. So let’s divide to get W/m2.

The sun delivers 750 W/m2 of power to the solar cell.Okay. A watt is a joule per second. So if I want an answer in joules, I need to multiply by seconds. There are 3600 seconds in an hour, 24 hours in a day.

The sun delivers 6.48 x 106 J to a square meter of the earth’s surface in a day!

1500 J/s 3600 s 24 h 6,480,000 J

2 m2 1 h 1 day