Fields & Static
- Objects with static charge create an electric field in the space around them
- If other charges enter the field then they will experience an electric force, attracting or repelling them from the object
- Therefore, an electric field can be defined as:
A region in which a charged object will experience an electric force
- Electric fields are represented by electric field lines that are always in the direction of positive to negative
- The electric field lines for a charged, isolated sphere, such as a spherical conductor:
- Point away from the centre of a positive sphere
- Point towards the centre of a negative sphere
- A uniform electric field, such as that between two parallel plates, are straight parallel lines from positive to negative:
Electric field lines between two parallel plates
- The electric field pattern between two oppositely charged spheres (or point charges) is slightly different and looks like:
Electric field pattern for two opposite charges
- The electric field helps to explain the non-contact force between charged objects since the electric field cannot be seen, but can be detected by another charged object that moves within that field due to the electric force
- This is a non-contact force because the charged objects do not touch for the force to be exerted
- If an electric field becomes strong enough, the charges are forced through insulators such as air, creating a spark
- This is what happens for example, when a charged person touches a conductor
- The charged particles will travel towards areas with the opposite charge
Positive and negative charges will travel towards the opposite charge, creating a spark
Exam Tip
Remember when drawing field lines to always include their direction with arrows pointing in the correct direction. If the field lines are straight, always use a ruler or a straight edge to draw them
In my experience of teaching electric fields to GCSE students, they tend to find the idea of fields quite tricky because we can't actually see them. In their very first GCSE lesson, I always tell my students that science is like a jigsaw puzzle with a thousand pieces. At first, it just seems like a jumble of separate pieces of information, but when you start linking those pieces together you begin to see the big picture.
In order to understand fields, it helps to know a little about forces. AQA have arranged this course so that electric fields come before forces and magnetism. However, you should have covered the basics in Key Stage 3.
All non-contact forces occur because of the presence of a field. Magnetism is a great example because, you can feel the force of attraction and repulsion when you bring two magnets close to one another, and because (with the help of some iron filings) you are able to see the field pattern. Electric fields work in the same way as magnetic fields. When you have a charged object, there is an electric field around it. If you place another charged object in that field, it experiences a force. Like charges will repel and opposite charges will attract.
The more links you make between topics as you study and revise this course, the deeper your understanding will grow across all topics. Mind maps are a great visual way to organise concepts that can be linked together.
