| Question | Answer |
| How fast does an electromagnetic wave move? | Speed of light. Continually self-reinforcing. Light is electromagnetic waves. |
| What makes up electromagnetic waves? | Vibrating electric and magnetic fields that regenerate each other. Electric field perpendicular to magnetic field. |
| How do you produce electromagnetic waves? | Shake a charged rod in space |
| Maxwell's law | A magnetic field is created in any region of space in which an electric field is changing with time. The magnitude of the created magnetic field is proportional to the rate at which the electric field changes. The direction of the created magnetic field is at right angles to the changing electric field. |
| power is transmitted great distances at: | high voltages and low currents |
| power in a transformer | rate at which energy is transferred |
| relationship between primary and secondary voltages | primary voltage/number of turns = secondary voltage/number of turns |
| step-down transformer | voltage produced in secondary lower than that in primary |
| step-up transformer | arrangement of greater number of turns on the secondary than on the primary |
| transformer | device for increasing or decreasing voltage through electromagnetic induction |
| Why does the current in a transformer intensify if you put a magnet through the primary and secondary loops | Alignment of magnetic domains in the iron, and the concentration of the magnetic field in the core |
| Secondary | Output, connected to a galvanometer |
| Primary | Input, coils connected to a power source. |
| Generator effect | When a wire with not initial current is moved downard, the electrons in the wire experience a deflecting force perpendicular to their motion. |
| What is the motor effect? | Moving charges experience a force that is perpendicualr to both their motion and the magnetic field they traverse. Stationary wire and magnet. |
| What usually powers turbines? | Steam |
| turbine | Connected to armature, produces its rotation. |
| What type of current does a generator induce? | Alternating |
| generator | converts mechanical energy into electric energy |
| Faraday's Law | The induced voltage in a coil is proportional to the product of the number of loops and the rate at which the magnetic field changes within these loops. or: An electric field is created in any region of space in which a magnetic field is changing with time. The magnitude of the created electric field is proportional to the rate at which the magnetic field changes. The direction of the created electric field is at right angles to the changing magnetic field. |
| electromagnetic induction | phenomenon of inducing voltage by changing magnetic field around a conductor |
| How does the law of conservation of energy hold true in electromagnetic induction | Input work equals energy expended in circuit to which the coil is connected. Harder to push magnet into more coils because current is greater and generates stronger magnetic field. |
| Amount of voltage produced by electromagnetic induction | Depends on how quickly magnetic field lines traversed by the wire. More loops, greater voltage. (Also, greater current) |
| Relative motion | Only thing that electromagnetic induction depends on. Doesn't matter whether magnet or wire moves, either. |
| Symbol for current flowing towards the reader | Dot |
| Symbol for current flowing away from the reader | X |
| How do you use the flat hand rule | Hold hand flat, with thumb at right angle. Fingers in direction of magnetic field, thumb in direction of moving charge, palm = force |
| When do you use the Flat Hand Rule | For finding the direction of the magnetic force acting on a charge moving across a magnetic field |
| What is conventional current | Flow of positive charge, even though does not flow. Old rule. Use right hand. |
| How do you use the curl hand rule | Thumb along the wire, curl fingers around wire to find direction of magnetic field, compass needle with point in that direction, tangent to the field lines |
| When is the curl hand rule used? | For finding the direction of the circular magnetic field around a current-carrying wire |
| Does the earth's magnetic field change? | Yes, quite often. Always changing, unpredictable. |
| Why is earth a magnet? | Don't really know. Could be molten currents beneath crust, moving charges. or convection currents combined with rotational effects of the earth. |
| magnetic declination | discrepancy between orientation of compass and true north |
| Where is the magnetic north pole? | About 1800 kilometers from geographic north pole |
| armature | many loops of wire wound about an iron cylander |
| brushes | brush against stationary contacts |
| Measures current | galvanometer |
| Current through magnetic field. Direction of current reversed? | Deflecting force. If reversed deflecting force in opposite direction. Maximum when perpendicular, zero when parallel. |
| What happens if a charged particle moves in a magnetic field | Experiences a deflecting force. Greatest when particle perpendicular to magnetic field lines, zero when parallel to magnetic field lines. Direction of force perpendicular to both magnetic field and velocity of charged particle. |
| superconducting electromagnet | generate powerful magnetic field indefinitely without using any power. Use superconducting wire instead of iron. |
| electromagnet | current-carrying coil of wire with many loops |
| What happens when you surround a current-carrying wire with compasses? When you reverse the direction of the current? | The compasses align with the magnetic field lines the moving charges create. Turn 180 degrees when current reversed. |
| How do you make a magnet? | Hold a strong magnet up to it for a very long time until the domains align. Helps to tap, stroke or nudge because helps to align domains. |
| magnetic domains | microscopic cluster of atoms with their magnetic fields aligned, domains perfectly magnetized |
| What creates a magnetic field? | Moving electric charges |
| A moving electric charge is surrounded by | An electric field and a magnetic field |
| magnetic field lines | lines that reveal the shape of a magnetic field. Direction: from north to south pole. Lines closer together indicate stronger field. |
| magnetic field | space around a magnet in which a magnetic field is exerted |
| basic law of magnitude | like poles repel, opposite poles attract |
| south-seeking pole | end that points south |
| north-seeking pole | end that points north |
| magnetic poles | regions that produce magnetic forces |
53 cards - created apr 29, 6:20pm