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Year 10 Electric Circuits
Learning Objectives

Students should understand the following:

• Circuit diagrams use standard symbols:
  
• Students should be able to draw and interpret circuit diagrams.
• For electrical charge to flow through a closed circuit the circuit must include a source of potential difference.
• Electric current is a flow of electrical charge. The size of the electric current is the rate of flow of electrical charge.
• Charge flow, current and time are linked by the equation: charge flow= current × time (Q = I t)
• A current has the same value at any point in a single closed loop.
• The current (I) through a component depends on both the resistance (R) of the component and the potential difference (V) across the component.
• The greater the resistance of the component the smaller the current for a given potential difference (pd) across the component.
• Questions will be set using the term potential difference. Students will gain credit for the correct use of either potential difference or voltage.
• Current, potential difference or resistance can be calculated using the equation: potential difference = current × resistance (V = I R)

• Students should be able to explain that, for some resistors, the value of R remains constant but that in others it can change as the current changes.
• The current through an ohmic conductor (at a constant temperature) is directly proportional to the potential difference across the resistor. This means that the resistance remains constant as the current changes.
  
• The resistance of components such as lamps, diodes, thermistors and LDRs is not constant; it changes with the current through the component.
• The resistance of a filament lamp increases as the temperature of the filament increases.
  
• The current through a diode flows in one direction only. The diode has a very high resistance in the reverse direction.
  
• The resistance of a thermistor decreases as the temperature increases.
• The applications of thermistors in circuits eg a thermostat is required.
• The resistance of an LDR decreases as light intensity increases.
• The application of LDRs in circuits eg switching lights on when it gets dark is required.
• Students should be able to:
  - explain the design and use of a circuit to measure the resistance of a component by measuring the current through, and potential difference across, the component
  - draw an appropriate circuit diagram using correct circuit symbols.
• Students should be able to use graphs to explore whether circuit elements are linear or non-linear and relate the curves produced to their function and properties.
• There are two ways of joining electrical components, in series and in parallel. Some circuits include both series and parallel parts.
• For components connected in series:
  - there is the same current through each component
  - the total potential difference of the power supply is shared between the components
  - the total resistance of two components is the sum of the resistance of each component.
  - R_total = R₁ + R₂
• For components connected in parallel:
  - the potential difference across each component is the same
  - the total current through the whole circuit is the sum of the currents through the separate components
• the total resistance of two resistors is less than the resistance of the smallest individual resistor.
• Students should be able to:
  - use circuit diagrams to construct and check series and parallel circuits that include a variety of common circuit components
  - describe the difference between series and parallel circuits
  - explain qualitatively why adding resistors in series increases the total resistance whilst adding resistors in parallel decreases the total resistance
  - explain the design and use of dc series circuits for measurement and testing purposes
  - calculate the currents, potential differences and resistances in dc series circuits
  - solve problems for circuits which include resistors in series using the concept of equivalent resistance.
  - Students are not required to calculate the total resistance of two resistors joined in parallel.
• LOGON SCIENCE codes - 4.2.1.1, 4.2.1.2, 4.2.1.3, 4.2.1.4, 4.2.2, 4.2.4.1, 4.2.4.2

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