Grade by Grade
D. Physics: Principles and Applications of Electricity · Electricity: Charges, Circuits and Energy

Electricity: Charges, Circuits and Energy: Unit Review

A1.1 A1.2 A1.4 A1.5 A2.2 A2.3 A2.4 D1.1 D1.2 D1.3 D1.4 D2.1 D2.2 D2.3 D2.4 D2.5 D2.6 D2.7 D2.8About 40 minutes
Learning goals
  • I can explain static electricity and charging using electrons and atomic structure, and classify conductors and insulators.
  • I can define and calculate current, potential difference, resistance, power and energy with the correct SI units.
  • I can use Ohm's law and the series and parallel rules to solve circuits.
  • I can explain electricity versus electrical energy, calculate efficiency, and assess how electrical energy is produced and conserved.

Words to know

electron
The negatively charged subatomic particle that moves when objects become charged and when current flows in a metal.
electric current (I)
Charge per second, in amperes (A).
potential difference (V)
Energy per unit of charge, in volts (V).
resistance (R)
Opposition to current, in ohms (Ω). R = V ÷ I.
Ohm's law
V = I × R.
efficiency
Useful output energy ÷ total input energy × 100%.
kilowatt-hour (kWh)
1 kW for 1 h = 3.6 million joules.

Let's review!

In this unit you explained static electricity with subatomic particles and the three ways of charging, tested conductors and insulators, defined current, potential difference and resistance with their units, built and drew DC circuits with meters, discovered Ohm's law by investigation and used it in real situations, compared series and parallel circuits, explained the difference between electricity and electrical energy, measured efficiency, and assessed how Ontario produces electrical energy and how we can use it more sustainably.

This review has a few questions from every lesson. Try each one, then press Show answer to check. If a part feels tricky, go back to that lesson.

I = Q ÷ tcurrent (A)V = E ÷ Qpotential difference (V)V = I × ROhm's lawP = V × Ipower (W)E = P × tenergy (J or kWh)useful ÷ total × 100%efficiency
The key formulas of the unit. Remember to convert to base units (A, V, Ω, s, J) first, or use kW and h together for kWh.
Series: one path+−I same everywhereV shared: V_T = V₁ + V₂R_T = R₁ + R₂Parallel: branches+−V same on every branchI splits: I_T = I₁ + I₂1/R_T = 1/R₁ + 1/R₂
Series versus parallel. In series, the current is the same and the voltage is shared. In parallel, the voltage is the same and the current is shared.

Electric Charge and the Atom

1

An object has 26 protons and 29 electrons. What is its net charge? Is it positive or negative?

2

A neutral rod becomes positive. Did it gain protons or lose electrons? Explain.

3

Ball A attracts ball B. Can you be sure both are charged?

4

A balloon has a charge of −3.2 × 10⁻⁸ C. How many extra electrons does it have?

Charging Objects: Friction, Contact and Induction

1

Wool is rubbed with a rubber balloon. Using the electrostatic series, which becomes negative?

2

A positive rod charges a neutral sphere by contact. What is the sphere's charge?

3

A positive rod charges a neutral sphere by induction. What is the sphere's charge, and which way do electrons move during grounding?

Conductors, Insulators and Testing Conductivity

1

Why do insulators hold static charge well?

2

In a continuity tester, a sample lights the LED. What is the sample?

3

Name the independent and dependent variables when testing the conductivity of different materials.

Current Electricity: Electric Current and Potential Difference

1

90 C of charge passes a point in 45 s. Find the current.

2

A 12 V battery gives energy to 5.0 C of charge. How much energy?

3

Which way do electrons flow outside a battery? Which way is conventional current?

4

Wall outlets in Canada supply AC or DC?

DC Circuit Components, Symbols and SI Units

1

How is a voltmeter connected, and why?

2

Give the symbol and unit for current and for potential difference.

3

What is the function of a fuse?

Resistance and the Factors That Affect It

1

List four factors that affect the resistance of a wire and say how each one increases resistance.

2

A 12 V source pushes 0.60 A through a component. Find R.

3

Why is a short circuit dangerous?

Investigating Current, Potential Difference and Resistance: Ohm's Law

1

A V–I graph (V on the y-axis) is a straight line through (0, 0) and (0.40 A, 10 V). Find R.

2

For a fixed resistor, V is doubled. What happens to I?

3

Is a filament lamp ohmic? Explain.

Applying Ohm's Law to Real-World Problems

1

A 9.0 V battery is connected to a 1.8 kΩ resistor. Find the current in mA.

2

A heater draws 12 A from 120 V. Find its resistance.

3

Use Ohm's law to explain why GFCI outlets are installed near sinks.

Series Circuits: Current, Potential Difference and Resistance

1

A 12 V battery is connected to 2.0 Ω and 4.0 Ω in series. Find R_T, I and the voltage across each.

2

Two resistors are in series with a 9.0 V battery. One has 3.5 V across it. What about the other?

3

What happens to the brightness of series lamps when another lamp is added?

Parallel Circuits and Comparing Series and Parallel

1

A 6.0 V battery is connected to 3.0 Ω and 6.0 Ω in parallel. Find each branch current, I_T and R_T.

2

Three 9.0 Ω resistors are in parallel. Find R_T.

3

Give two reasons homes are wired in parallel.

Electricity Versus Electrical Energy: Power and the Kilowatt-Hour

1

Explain the difference between electricity and electrical energy.

2

A 1.2 kW heater runs 5.0 h. How many kWh? Cost at 10¢/kWh?

3

A device draws 0.50 A at 120 V. What is its power?

Energy Transformations and the Efficiency of Electrical Devices

1

A motor uses 1200 J and produces 900 J of kinetic energy. Efficiency?

2

Name the energy transformation in a generator and in a solar panel.

3

Where does the wasted energy usually go?

Producing Electrical Energy: Sources, Benefits and Challenges

1

About what share of Ontario's electricity came from nuclear in 2024?

2

Give one benefit and one challenge of wind power.

3

Explain how connecting remote First Nations to the provincial grid affects those communities.

Emerging Technologies, Conservation and a Plan of Action

1

A 4 W standby load runs all year. How many kWh?

2

Give one social, one environmental and one economic impact of grid-scale batteries.

3

Rewrite "Save energy at home" as a SMART goal.

Just for fun

Two electrons were arguing about which circuit was better. Finally one said: "Fine, let's just agree to go our separate ways."

The other one replied: "That's the most parallel thing you've ever said."

How to use this review

  • Do the review without your notes first, then check each answer.
  • Mark every question you missed and note which lesson it came from.
  • Go back to that lesson's worked examples, then redo its "More practice" sets.
  • For calculation questions, always write the formula, substitute with units, and check that the answer makes sense (for example, V₁ + V₂ = V_T in series).
  • Finish with the 10-question quiz below.
Check your understanding

Quiz

1.

A neutral object gains electrons. It becomes:

2.

Charging by induction gives an object:

3.

Which material is a good conductor?

4.

The SI unit of resistance is the:

5.

A 24 V supply pushes 3.0 A through a resistor. R =

6.

Resistors of 10 Ω and 30 Ω in series have a total resistance of:

7.

In a parallel circuit, which quantity is the same for every branch?

8.

What do electricity bills charge for?

9.

A kettle uses 400 kJ and 340 kJ goes into the water. Its efficiency is:

10.

Which source supplied the largest share of Ontario's electricity in 2024?

For parents and teachers

How to use the review results:

  • Mistakes with protons and electrons, or net charge → revisit Electric Charge and the Atom.
  • Mixing up contact and induction, or the electrostatic series → revisit Charging Objects: Friction, Contact and Induction.
  • Confusing conductors and insulators, or fair-test variables → revisit Conductors, Insulators and Testing Conductivity.
  • Errors with I = Q ÷ t or V = E ÷ Q, or unit conversions to seconds → revisit Current Electricity: Electric Current and Potential Difference.
  • Meters in the wrong place, or wrong units and symbols → revisit DC Circuit Components, Symbols and SI Units.
  • Thinking thicker wires resist more, or confusion about short circuits → revisit Resistance and the Factors That Affect It.
  • Trouble with slopes, graphs, or ohmic vs non-ohmic → revisit Investigating Current, Potential Difference and Resistance: Ohm's Law.
  • Rearranging V = I × R, or mA and kΩ conversions → revisit Applying Ohm's Law to Real-World Problems.
  • Adding currents in series, or voltages that do not add up → revisit Series Circuits.
  • Adding resistances in parallel, or forgetting to flip 1/R_T → revisit Parallel Circuits and Comparing Series and Parallel.
  • Saying "current gets used up", or kWh errors → revisit Electricity Versus Electrical Energy.
  • Efficiency above 100%, or missing energy transformations → revisit Energy Transformations and the Efficiency of Electrical Devices.
  • One-sided answers about energy sources → revisit Producing Electrical Energy.
  • Vague goals or missing data in a plan of action → revisit Emerging Technologies, Conservation and a Plan of Action.

Keep practice short and regular, and ask your teen to explain one circuit or one energy choice out loud each day: explaining clearly is part of Grade 9 science communication.