Electric Fields

    OCR
    GCSE

    An electric field is defined as a region of space where a charged object experiences a non-contact force. The direction of the field at any point is the direction of the force on a positive test charge, represented by field lines that diverge from positive charges and converge on negative ones. The strength of the field is determined by the charge magnitude and distance, adhering to inverse-square principles for point charges and remaining constant in uniform fields between parallel plates. Understanding these fields is critical for explaining electrostatic phenomena, capacitance, and the motion of charged particles in vacuums.

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    Objectives
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    Exam Tips
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    Pitfalls
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    Key Terms
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    Mark Points

    What You Need to Demonstrate

    Key skills and knowledge for this topic

    • Award 1 mark for stating that friction causes the transfer of electrons from one insulator to another
    • Award 1 mark for drawing electric field lines directed radially away from a positive charge and towards a negative charge
    • Credit responses that show field lines drawn perpendicular to the surface of the charged object
    • Award 1 mark for explicitly linking the closer spacing (density) of field lines to a stronger electric field
    • Award 1 mark for explaining sparking (Higher Tier): high potential difference creates a strong field that ionises air, allowing charge to flow

    Example Examiner Feedback

    Real feedback patterns examiners use when marking

    • "You have correctly identified the direction of the force, but you must reference 'electron transfer' rather than just 'charge moving'"
    • "Your field lines are correct in direction, but ensure they are perpendicular to the surface to secure the accuracy mark"
    • "Good explanation of repulsion. To improve, explicitly state that the object creates an electric field in which the other object experiences a force"
    • "For this Higher Tier question, you missed the link between strong electric fields and the ionisation of air molecules"

    Marking Points

    Key points examiners look for in your answers

    • Award 1 mark for stating that friction causes the transfer of electrons from one insulator to another
    • Award 1 mark for drawing electric field lines directed radially away from a positive charge and towards a negative charge
    • Credit responses that show field lines drawn perpendicular to the surface of the charged object
    • Award 1 mark for explicitly linking the closer spacing (density) of field lines to a stronger electric field
    • Award 1 mark for explaining sparking (Higher Tier): high potential difference creates a strong field that ionises air, allowing charge to flow

    Examiner Tips

    Expert advice for maximising your marks

    • 💡When asked to draw field lines, always use a ruler for radial lines and ensure arrows clearly point from Positive to Negative
    • 💡For Higher Tier questions on sparking, you must use the terms 'potential difference', 'ionisation', and 'conductive path' for full marks
    • 💡Distinguish clearly between the cause of the charge (electron transfer) and the effect of the charge (force in a field)

    Common Mistakes

    Pitfalls to avoid in your exam answers

    • Stating that positive charges (protons) move during friction; candidates must specify electron transfer
    • Drawing electric field lines that cross each other or fail to touch the surface of the charged object
    • Describing the force as 'magnetic' rather than 'electrostatic' or 'electric'
    • Vaguely stating the field is 'stronger near the charge' without referencing the spacing of the field lines as the evidence

    Study Guide Available

    Comprehensive revision notes & examples

    Read Study Guide

    Key Terminology

    Essential terms to know

    Non-contact electrostatic forces (attraction and repulsion)
    Electric field representation (field lines and patterns)
    Electric field strength (E = F/Q)
    Uniform versus radial fields
    Electrical potential and work done

    Likely Command Words

    How questions on this topic are typically asked

    Draw
    Describe
    Explain
    Suggest
    Compare

    Practical Links

    Related required practicals

    • •{"code":"P2.3 Investigation","title":"Static Electricity Experiments","relevance":"Demonstrating attraction/repulsion using polythene and acetate rods to verify field concepts"}

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