4.3.1
Fields
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Force Fields
Fields are a convenient mathematical idea for representing how forces and potential energies change in a region of space around an object. Forces arise from the interactions between objects.

Gravitational force
- Gravitational force arises because of the interaction between two masses.
- We map gravitational fields by considering the effect of that field on a point mass.

Electrostatic force
- Electrostatic force arises because of the interaction between two charges.
- We map electric fields by considering the effect of that field on a point positive charge.

Magnetic force
- Magnetic force arises, fundamentally, because of the interaction between charges that have relative motion between them.
- When we map magnetic fields, we simplify matters by considering the effect on a small bar magnet, or magnetic dipole.
Comparing Gravitational and Electrostatic Forces
Gravitational and electrostatic forces have similarities and differences.

Similar ideas
- If we consider both as fields, we can apply similar ideas.
- We use field lines to represent the direction of the force on a point particle.
- We use the concept of equipotential lines and surfaces.

Similarities
- When considering point objects, both forces have inverse-square laws.
- The field line patterns around point objects are radial - like spokes on a bicycle wheel.
- The field lines get further apart as the distance increases from the point object. This indicates that the force on a test particle gets smaller.
Similarities 2
- Equipotential lines/surfaces around point objects are concentric circles or spheres.
- Those equipotential lines get further apart for equal changes in potential between lines.
- You can add field strengths from two or more particles vectorially. This means you can determine field line patterns from complex arrangements of particles.

Differences
- The force between masses is always attractive.
- Field lines always point towards masses.
- Potential-distance graphs for gravitation are always negative.
- The force between charges can be either attractive or repulsive.
- Field lines always point away from positive charges and towards negative charges.
- Potential-distance graphs for a point charge can either be positive or negative.
1Space, Time & Motion
1.1Motion
1.2Forces
1.3Momentum & Impulse
2The Particulate Nature of Matter
2.1Thermal Concepts
3Wave Behaviour
3.1Oscillations
3.2Travelling Waves
3.3Wave Characteristics
3.4Wave Behaviour
3.5Standing Waves
3.6Simple Harmonic Motion
3.7Single Slit Diffraction
3.8Interference
3.9Doppler Effect
4Fields
4.1Circular Motion
4.2Newton's Law of Gravitation
4.3Fields
4.4Fields at Work
4.5Electric Fields
4.6Magnetic Effect of Electric Currents
4.7Heating Effect of Currents
4.8Electromagnetic Induction
4.9Power Generation & Transmission
5Nuclear & Quantum Physics
5.1Discrete Energy & Radioactivity
5.2Nuclear Reactions
5.3The Interaction of Matter with Radiation
6Measurements
6.1Measurements & Errors
6.2Uncertainties & Errors
6.3Vectors & Scalars
Jump to other topics
1Space, Time & Motion
1.1Motion
1.2Forces
1.3Momentum & Impulse
2The Particulate Nature of Matter
2.1Thermal Concepts
3Wave Behaviour
3.1Oscillations
3.2Travelling Waves
3.3Wave Characteristics
3.4Wave Behaviour
3.5Standing Waves
3.6Simple Harmonic Motion
3.7Single Slit Diffraction
3.8Interference
3.9Doppler Effect
4Fields
4.1Circular Motion
4.2Newton's Law of Gravitation
4.3Fields
4.4Fields at Work
4.5Electric Fields
4.6Magnetic Effect of Electric Currents
4.7Heating Effect of Currents
4.8Electromagnetic Induction
4.9Power Generation & Transmission
5Nuclear & Quantum Physics
5.1Discrete Energy & Radioactivity
5.2Nuclear Reactions
5.3The Interaction of Matter with Radiation
6Measurements
6.1Measurements & Errors
6.2Uncertainties & Errors
6.3Vectors & Scalars
Practice questions on Fields
Can you answer these? Test yourself with free interactive practice on Seneca — used by over 10 million students.
- 1Name three types of fields:Fill in the list
- 2Which force arises due to the interaction between masses?Multiple choice
- 3
- 4
- 5Which of the following are types of fields?True / false
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