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Effects of electric current An electric current that flows in a conductor has a number of effects: 1. HEATING The friction caused by the current causes the conductor to heat up. The greater the current the more heat is generated. 2. MAGNETIC EFFECT - A magnetic field is generated around any conductor when an electric current flows through it. Magnetic Effect A magnetic field is generated around any conductor when an electric current flows through it. Electric current Magnetic field Wire with current coming towards you Right Hand Wire Rule>>> Wire with current going away from you x Right Hand Wire Rule Magnetic Effect A magnetic field is generated around any conductor when an electric current flows through it. Electric current Wire with current coming towards you Wire with current going away from you x SOLENOID A coil generates a very concentrated (strong) magnetic field in its center. Increasing the Electric current number of coils strengthens the magnetic field. N x The Right Hand Rule can also be applied to a solenoid! x S x INSIDE THE COIL THE FIELD GOES FROM SOUTH TO NORTH!!! Right Hand Rule - Solenoid Solenoid Field Web Applet Demo>> Note field same as bar magnet Inside S N!!!!! Electromagnetic Induction - An electrical conductor that is accelerated through a magnetic field will experience an INDUCED electrical current according to Fleming's Right Hand Rule. Thrust Thumb Field Forefinger Second Current N + S Thrust Faraday’s Law The size of the induced current is directly proportional to the rate of change of the magnetic flux linkage. Electric Field Strength + Magnetic field Strength (B) measured in ……………… (………) Total number of field lines is called ………………….. (…….) measured in ………………. (……) = ………. = ………………….. (………) B = ……………………. (……) A = ………………. through which flux passes - (…...) N (… ….) S Thrust (…..) = no of ………. in that area. 1 ………….. is the field ……………. when a current of …….. A flows through a conductor and it experiences a ………….. of …N per meter of length. Electric Field Strength + Magnetic field Strength (B) measured in Tesla’s (T) Total number of field lines is called magnetic flux () measured in Webers (Wb) = BA = magnetic flux (Wb) B = magnetic field strength (T) A = area through which flux passes (1A) (1T) N S Thrust (1N) = no lines in that area 1 Tesla is the field strength when a current of 1 A flows through a conductor and it experiences a force of 1N per meter of length. Faraday’s Law The induced emf (….) is directly proportional to the …………. of change of ………………….. N t S N The induced emf can be increased by: • Increasing the ………………… • Using ……………………… • Decreasing the …………. – moving ……….. The size of the induced ……………… is (also) directly proportional to the ………………………. of the ……………………………………... Faraday’s Law The induced emf () is directly proportional to the rate of change of flux linkage. N t S N The induced emf can be increased by: • Increasing the number of coils • Using stronger magnets • Decreasing the time – moving faster The size of the induced current is (also) directly proportional to the rate of change of the magnetic flux linkage. Electric Guitar Lenz’s Law The induced field …….. (………………) is induced in such a way as to ……………… the ……… causing it. Lenz’s Law S N S N N S N S The induced field B (S N) is induced in such a way as to oppose the action causing it. THE MOTOR EFFECT - + A current carrying conductor in a magnetic field experiences a ……………. The direction is given by ……………………………….. ………. rule. Second ………. Thumb N S Forefinger ……….. Magnetic fields …………………….. Fields in opposite direction they ………………………… ………………… - resulting in a …………………….. force. N X S THE MOTOR EFFECT - + A current carrying conductor in a magnetic field experiences a force. The direction is given by Fleming's Left Hand Motor Current rule. Second Thrust Thumb N Forefinger Field S Force Magnetic fields strengthened! Fields in opposite direction they cancel out/become weakened - resulting in a downward force. N X X S THE ELECTRIC MOTOR current B C N S - A + D THE ELECTRIC MOTOR current B C Current Field Thrust S N A + D - THE ELECTRIC MOTOR C B current BB CC Current C Field ThrustD N B - AA + D DD A A S THE ELECTRIC MOTOR Mutual Induction ~ MUTUAL INDUCTION is defined as the changing electric …………………… producing a changing …………………….. field which can produce a changing ………………….. in another conductor. This is the basic principle of the ……………………… Mutual Induction ~ MUTUAL INDUCTION is defined as the changing electric current producing a changing magnetic field which can produce a changing current in another conductor. This is the basic principle of the TRANSFORMER Transformers Coils of insulated conducting wire are wound around a ring of iron constructed of thin isolated laminations or sheets. The laminations minimize eddy currents in the iron. Eddy currents are circulatory currents induced in the metal by the changing magnetic field. These currents produce an undesirable by-product—heat in the iron. Energy loss in a transformer can be reduced by using thinner laminations, very “soft” (low-carbon) iron and wire with a larger cross section, or by winding the primary and secondary circuits with conductors that have very low resistance. Transformers used to transmit and distribute power are commonly 98 to 99 percent efficient. While eddy currents are a problem in transformers, they are useful for heating objects in a vacuum. Transformers Transformers Ideally – all magnetic flux from primary coil links with secondary coil. The number of turns of wire is directly proportional to the voltage in the coil. Np Vp — = — Ns Vs How many turns of wire would you need in a transformer that has 1000 turns in the primary and needs to step down the voltage from 220V to 9V? Transformers Ideally – all magnetic flux from primary coil links with secondary coil. From Faraday’s Law: “The size of the induced current is directly proportional to the rate of change of the magnetic flux linkage.” Therefore: work done by primary = energy gained by secondary Since W = QV and Q = It .: W = VIt Wp = Ws VpIpt = VsIst VpIp = VsIs P p = Ps Calculate the current in the secondary coil of the 220V/9V transformer if the current in the primary was 1.5A