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Physics Definitions Start from R

Radiation Belt - A ring-shaped region around a planet in which electrically charged particles (usually electrons and protons) are trapped. The particles follow spiral trajectories around the direction of the magnetic field of the planet. The radiation belts surrounding Earth are known as the Van Allen belts.

Relativistic - Describes anything traveling at nearly the speed of light, and obeying the special laws of behavior that apply at such speeds.

RHIC - The Relativistic Heavy Ion Collider, a physics research machine at Brookhaven National Laboratory. Will collide two beams of atomic nuclei at 99.95 percent the speed of light.

Radiation - Electromagnetic waves that carry energy.

Radioactive Decay - Spontaneous change of unstable nuclei into other nuclei.

Radioactive Materials - Materials that undergo radioactive decay.

Range of Projectile - Horizontal distance between launch point of projectile and where it returns to launch height.

Ray model of light - Light may be represented by straight line along direction of motion.

Ray Optics - Study of light using ray model.

Rayleigh Criterion - Two optical images are separable if central bright spot of one image falls on first dark band of second.

Real Image - Optical image at which rays from object converge.

Receiver - Device that detects electromagnetic waves.

Reference Level - Location at which potential energy is chosen to be zero.

Reference Point - Zero location in a coordinate system or frame of reference.

Refraction - Change in direction of light ray when passing one medium to another.

Refractive Index - Ratio of speed of light in vacuum to that in the medium.

Resistance - Ratio of potential difference across device to current through it.

Resistance Force - Force exerted by a machine.

Resistor - Device designed to have a specific resistance.

Responding Variable - Variable that changes as result of change in manipulated variable.

Rest Energy - Energy due to mass of object; E= mc^ 2.

Resultant - Vector sum of two or more vectors.

Right-Hand Rules - Used to find force on current or moving particle in magnetic field; used to find direction of magnetic field caused by current or of induced EMF.

Rutherford’s Model of Atom - Nuclear model of atom; essentially all mass in compact, positively- charged object at center, surrounded by electrons.

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