RESISTANCE

Electrical resistance KS3 | Y9 Science Lesson Resources | Oak National Academy

KEY WORDS AND DEFINITIONS – RESISTANCE (YEAR 7 PHYSICS)

• RESISTANCE: The opposition to the flow of electric current in a circuit.

• ELECTRIC CURRENT: The flow of electric charge through a circuit.

• CHARGE: The electricity carried by particles, usually electrons, in a circuit.

• CONDUCTOR: A material that allows electric current to flow easily (for example, copper).

• INSULATOR: A material that does not allow electric current to flow easily (for example, plastic).

• METAL: A material that usually has low resistance and is a good conductor of electricity.

• NON-METAL: A material that usually has high resistance and is a poor conductor of electricity.

• WIRE: A metal path that allows electric current to flow in a circuit.

• THICK WIRE: A wire with low resistance because it allows charge to flow more easily.

• THIN WIRE
  A wire with higher resistance because it makes it harder for charge to flow.

• OHM (Ω): The unit used to measure resistance.

• CIRCUIT: A complete path that allows electric current to flow.

• BULB (LAMP): A component that converts electrical energy into light and heat.

• SAFETY DEVICE: A component that uses resistance to help prevent too much current flowing (for example, a fuse)

WHAT ELECTRIC CURRENT IS

In a circuit, electric current is the movement of electricity from the power source, through the wires, and back again. This movement happens because tiny particles called electrons carry charge. When a circuit is complete, charge can flow all the way around it. If the circuit is broken, the charge cannot move and the current stops. The current is what allows electrical devices like bulbs and buzzers to work.

WHAT RESISTANCE MEANS

Resistance is how much something slows down the flow of electric current in a circuit. When there is a lot of resistance, charge finds it harder to move through the circuit, so the current is smaller. When there is less resistance, charge can move more easily, so the current is larger. Resistance does not stop the current completely, but it controls how easily the current can flow.

CONDUCTORS AND INSULATORS

Different materials affect resistance in different ways. A conductor is a material that allows electric current to flow easily because it has low resistance. Metals such as copper are good conductors, which is why wires are made from metal. An insulator is a material that does not allow current to flow easily because it has high resistance. Plastic is a good insulator and is often used to cover wires to keep people safe from electric shocks.

METALS AND NON-METALS

Metals usually have low resistance because charge can move through them easily. This makes them useful in circuits where we want current to flow. Non-metals usually have high resistance, meaning they make it harder for current to flow. This is why most non-metals are not used to carry electricity, but instead are used for insulation or protection.

WIRES AND RESISTANCE

The wire in a circuit is the path that the electric current follows. The thickness of a wire affects its resistance. A thick wire has low resistance because there is more space for charge to move through. A thin wire has higher resistance because charge has less space and is slowed down more. This means thicker wires allow more current to flow than thinner wires made from the same material.

MEASURING RESISTANCE

Resistance is measured in a unit called the ohm, which has the symbol Ω. Using ohms allows scientists to compare how much different components resist the flow of current. Components with a large number of ohms have high resistance, while components with a small number of ohms have low resistance.

RESISTANCE IN CIRCUITS AND DEVICES

A circuit is a complete path that allows electric current to flow. Components added to a circuit can increase resistance. For example, a bulb uses resistance to slow down the current. This causes the electrical energy to be changed into light and heat. If the resistance in a circuit increases, the current decreases and the bulb becomes dimmer.

RESISTANCE AND SAFETY

Resistance is also important for safety. A safety device such as a fuse uses resistance to protect a circuit. If too much current flows, the fuse heats up and breaks the circuit, stopping the current. This prevents damage to electrical devices and reduces the risk of fir

RESISTANCE – YEAR 7 PHYSICS QUESTIONS

ELECTRICITY IN CIRCUITS

WHAT IS HAPPENING IN A CIRCUIT?

Electrons already exist inside metal wires. In a normal wire that is not part of a working circuit, these electrons move randomly in all directions. Because their movement is random, there is no overall flow in one direction.

When we connect a complete circuit with a battery, something important changes. The electrons stop moving randomly and begin to drift in one direction around the circuit. This overall directed movement is called current.

Current is not “created” in the wire — it is already present as electrons. What changes is whether their movement is random or directed.

WHY DO ELECTRONS START MOVING IN ONE DIRECTION?

The change happens because of the battery.

Inside a battery, chemical reactions occur between different materials. These reactions move electrons from one side of the battery to the other. One side ends up with an excess of electrons (negative side), and the other side ends up with fewer electrons (positive side).

This is important: the battery is constantly forcing electrons to separate, even as they move around the circuit.

Because electrons are negatively charged, they repel each other. So when extra electrons are pushed onto the negative side, they are under pressure to spread out. At the same time, the positive side has fewer electrons and attracts them.

So when a wire is connected, electrons have a complete path to move from the negative side back to the positive side. This creates a continuous flow.

WHAT IS VOLTAGE REALLY DOING?

Voltage is the size of this separation effect created by the battery.

A key point is that voltage is not “stored electrons” or “extra charge sitting in the battery”. Instead, it is an energy difference created by the chemical reactions inside the battery.

A 1.5 V battery creates a small energy difference between its two ends. This means each electron that moves through the circuit is given a relatively small amount of energy to drive its movement.

A 9 V battery creates a much larger energy difference. This means each electron is driven much more strongly when it moves through the circuit.

So voltage is really about how much energy each unit of charge gains as it moves from one side of the battery to the other.

That is why we describe voltage as a “push”: a larger energy difference results in a stronger driving effect on electrons.

WHY DON’T ELECTRONS JUST FLOW FREELY?

Even though electrons are being pushed by the battery, they do not move smoothly through the wire.

As they move, they constantly collide with atoms in the metal. These atoms are arranged in a lattice and are vibrating. Every collision transfers energy from the moving electrons to the atoms in the wire.

This slows the electrons down and reduces how easily they can move through the material.

WHAT IS RESISTANCE?

Resistance is the effect of these collisions that oppose the movement of electrons.

It is not a force itself, but a measure of how strongly a material resists the flow of charge.

Resistance increases when:

• the wire is longer (more collisions happen)

• the wire is thinner (electrons are more crowded)

• the material is less conductive (atoms interfere more with electron motion)

• the temperature is higher (atoms vibrate more and cause more collisions)

HOW DO VOLTAGE, CURRENT AND RESISTANCE WORK TOGETHER?

Voltage provides the energy that drives electrons through the circuit.

Current is the resulting flow of electrons caused by that drive.

Resistance is what opposes that flow by causing energy loss through collisions.

So in every circuit, there is a constant balance between how strongly electrons are driven and how strongly their movement is resisted.

QUESTIONS

Year 7 Electricity Questions

MULTIPLE CHOICE

1. What is electrical resistance?
   a) The flow of electric charge
   b) The opposition to the flow of electric current
   c) A type of battery
   d) A kind of wire

2. Which material usually has high resistance?
   a) Copper
   b) Aluminium
   c) Plastic
   d) Iron

3. What unit is resistance measured in?
   a) Volts (V)
   b) Amps (A)
   c) Ohms (Ω)
   d) Watts (W)

SHORT ANSWER

4. What happens to the current when resistance increases?

5. Name one conductor and one insulator.

6. Why do long wires have more resistance than short wires?

FILL IN THE BLANKS

7. Resistance slows down the flow of electric __________.

8. Metals usually have __________ resistance than non-metals.

9. The symbol for resistance is __________.

EXPLAIN YOUR ANSWER

10. Why does a bulb glow dimmer when resistance in a circuit is increased?

11. How does resistance help make electrical devices safe?

CHALLENGE QUESTION

12. A thin wire and a thick wire are made of the same metal and have the same length.
    Which one has more resistance, and why?

Potential Difference (Voltage)

1. What is another name for potential difference?

2. What unit is used to measure voltage?

3. A battery has a voltage of 9 V. What does “9 V” mean?

4. Which device measures voltage?

• a) Ammeter

• b) Thermometer

• c) Voltmeter

5. Is voltage measured in:

• a) Amps

• b) Volts

• c) Ohms

AC and DC

6. What does DC stand for?

7. What does AC stand for?

8. Which type of current comes from batteries?

9. Which type of current comes from wall sockets in homes?

10. True or False:
    AC changes direction repeatedly.

11. True or False:
    DC flows in one direction only.

3. Current

12. What is electric current?

13. A current of 3 A flows through a lamp. What does “3 A” mean?

14. In a series circuit, does the current stay the same or change?

4. Resistance

17. What is resistance?

18. What unit is used to measure resistance?

19. Which material usually has HIGH resistance?

• a) Copper

• b) Plastic

• c) Silver

20. True or False:
    Thin wires usually have more resistance than thick wires.

21. What happens to current if resistance increases?

🔢 Calculation Questions

Find the Resistance

22. A bulb has a voltage of 12 V and a current of 3 A.
    What is the resistance?

23. A toaster uses 10 V and 2 A.
    Calculate the resistance.

24. A circuit has 20 V and 5 A.
    Find the resistance.

Find the Current

25. A circuit has 12 V and 4 Ω resistance.
    Find the current.

26. A lamp has 24 V and 6 Ω resistance.
    Calculate the current.

27. A motor uses 15 V with 3 Ω resistance.
    What is the current?

Find the Voltage

28. A current of 2 A flows through a 5 Ω resistor.
    Find the voltage.

29. A current of 4 A flows through a 3 Ω resistor.
    Calculate the voltage.

30. A resistor has 8 Ω resistance and 2 A current.
    What is the voltage?