Electromagnetic induction, transformers and Astrophysics I

When a wire cuts through magnetic field lines…

A potential difference (voltage) is induced across the ends of the wire.

This causes a current to flow (if there is a circuit).

What does the wire or magnet have to do for this to work?

It has to be MOVED.

What are the three ways to increase the size of the potential difference (and therefore current) ?

1. Using a stronger magnetic field

2. Having more turns on the coil of wire

3. Moving the wire faster

How can the direction of the potential difference (and thus current) be changed?

Switching the direction of the magnet poles or moving the wire I the opposite direction.

Some diagrams

Oscilloscope Trace Graph

If the base is 20 ms then every square across it is 20ms.

If the volts/div is 2.5, it means that every square is worth up to 2.5 volts.

How to calculate frequency/ how long one wave takes:

How to calculate peak voltage:

What is the easiest way to create electricity using magnets and wires?

Rotate the magnet or the wire.

this results in an alternating current being produced.

How a generator works:

Coil Cut Pot Up/Down Alt

Coil rotates

The side wires cut through the magnetic field.

A potential difference is induced across the coil (and current flows if in a circuit).

Each wire cuts UP, then DOWN, etc.

So, current is ALTERNATING.

Transformer diagram and defintion:

Two coils wrapped around a core with an alternating magnetic field.

How does a transformer work [SET PIECE]

AC AM FS AP AC

Alternating current in the PRIMARY COIL.

Produces an alternating magnetic field on the iron core.

The iron core makes the field STRONGER.

The alternating field induces an alternating potential difference in the SECONDARY COIL.

This produces an alternating current in the SECONDARY COIL circuit.

Why does direct current not work?

Because magnetic field does not change.

How can the transfer be enhanced?

By putting a magnetic core (iron, cobalt or nickel) through the centre of both coils.

How can step up or step down transformers be created?

By varying the number of turns on the coils.

How is a step UP transformer created?

More turns on the secondary than the primary coil.

More voltage on the secondary than the primary coil.

How is a step DOWN transformer created?

More turns on the primary than the secondary coil.

More voltage on the primary than the secondary coil.

Transformer Equation

The energy and power on both sides of the transformer is…

EQUAL because whilst the voltage goes up, the current goes down.

Transformer Voltage and Current Equation:

V_PI_P = V_SI_S

_{ALSO: P=I²R}

What is gravitational field strength measures in?

Newtons per Kilogram (N/Kg)

Earth = 10

Moon = 1.6

What affects gravitational field strength?

Size of the celestial body (mass)

Distance from the centre of the body

Wight vs Mass

MASS is the amount of matter in you and CANNOT CHANGE.

WEIGHT is the force due to gravity acting on your mass and CAN CHANGE.

Weight equation:

Weight (N) = Mass (kg) x Gravitational Field Strength (N/Kg)

Why do satellites stay in orbit?

They orbit in a circular or elliptical path and are constantly accelerating towards the body that they orbit.

Gravitational force keeps them in orbit.

How does gravity cause (nearly) circular motion?

It provides the centripetal force which pulls and object towards the centre of the “circle” and keeps it moving in a “circular” path.

Orbital Speed Equation:

V (m/s) = 2πr (m) / T (s)

Where r is the radius of the orbit and T is the time orbit for a full orbit.

V = orbit speed

The closer a planet is to the Sun…

the faster it moves as gravity is stronger closer in

What happens when a comet approaches the Sun?

The Sun heats up the comet’s surface.

Ice sublimates and dust and gas blast off the surface.

This creates a glowing coma and two long tails.

Comet tails always…

point away from the Sun.

Comet orbits

Highly elliptical

Spend most of their time far from the Sun

Only visible for a few months when near the Sun

Doppler shift diagram:

Doppler Shift Equation:

Redshift

Objects moving away.

Wavelength lengthening.

Appears more red.

Blueshift

Object coming towards.

Wavelength shortening.

Appears more blue.