Edexcel A-Level Physics 9PH0
Working as a Physicist
Mechanics
Electric Circuits
Materials
Waves and Particle Nature of Light
Further Mechanics
Electric and Magnetic Fields
Nuclear and Particle Physics
Thermodynamics
Space
Nuclear Radiation
Gravitational Fields
Oscillations
Further Mechanics
The radian, angular displacement and angular velocity
- 2 things to know
- Papers 1 and 3
Overview
Recall questions on the definition of the radian, converting between degrees and radians, the arc-length relationship, and the definitions of angular displacement and velocity.
What you need to know
Answer each one before you reveal it.
What are angular displacement and angular velocity, and what is the unit of angular velocity?
Questions from this subtopic
Each one with the model answer underneath.
- 1
Define the radian:
Model answer
One radian is the angle subtended at the centre of a circle by an arc whose length is equal to the radius of that circle.
- 2
How many radians are there in one complete revolution?
Model answer
There are 2π radians in a full revolution, which is about 6.28 rad.
- 3
How do you convert an angle from degrees into radians?
Model answer
Multiply the angle in degrees by π/180, because 180° is equal to π rad.
- 4
What is 45° expressed in radians?
Model answer
45 × π/180 = π/4 rad, which is 0.785 rad to 3 significant figures.
- 5
What is 2.0 rad expressed in degrees?
Model answer
2.0 × 180/π = 115° to 3 significant figures.
- 6
State the relationship between arc length, radius and angle:
Model answer
The arc length is given by s = rθ, where θ is the angle at the centre measured in radians.
Other ways to work this
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