Download presentation

Presentation is loading. Please wait.

Published byElijah Griffin Modified over 5 years ago

1
Electric current and direct-current circuits A flow of electric charge is called an electric current.

2
Electric current and direct-current circuits

4
When electric charge flows through a closed path and returns to its starting point the path is called an electric circuit.

5
Electric current and direct-current circuits When electric charge flows through a closed path in one direction the path is called a direct-current circuit.

6
Electric current and direct-current circuits When electric charge flows through a closed path and periodically reverses direction the path is called a alternating-current circuit.

7
Electric current and direct-current circuits A battery produces a difference in electric potential between its terminals through chemical reactions.

8
Electric current and direct-current circuits The symbol for a battery is

9
Electric current and direct-current circuits The terminal designated + corresponds to the higher potential, while the terminal designated by a – corresponds to the lower potential.

10
Electric current and direct-current circuits By convention we say that the direction of the current is the direction in which a positive charge would move.

11
Figure 21-4 Direction of Current and Electron Flow

12
Electric current and direct-current circuits The electromotive force (emf) (ξ) is the potential across the terminals (voltage) of a battery under ideal conditions.

13
Electric current and direct-current circuits The charges that actually move through a conductor, are electrons.

14
Electric current and direct-current circuits In a real conductor there is always some resistance to electron flow, and a potential difference is necessary to keep them flowing.

15
Electric current and direct-current circuits Ohm’s Law relates the potential(V), resistance (R)and current (I)in a circuit

16
Electric current and direct-current circuits Ohm’s Law

17
Electric current and direct-current circuits Ohm’s Law

18
Electric current and direct-current circuits Ohm’s Law

19
Electric current and direct-current circuits Ohm’s Law Unit for resistivity is

20
Electric current and direct-current circuits When an electric charge moves across a potential difference the potential energy changes by the amount

21
Electric current and direct-current circuits SI unit; watt, W

22
Electric current and direct-current circuits Other expressions for electric power

23
Electric current and direct-current circuits Other expressions for electric power

24
Electric current and direct-current circuits Resistors in a series are connected end to end.

25
Example 21-5 Three Resistors in Series

26
Electric current and direct-current circuits The equivalent resistance for resistors in series is just the sum of the individual resistances

27
Electric current and direct-current circuits For the example given

28
Electric current and direct-current circuits Each of the resistors connected in series has the same current going through it.

29
Electric current and direct-current circuits Resistors connected in parallel are connected across the same potential difference.

30
Example 21-6 Three Resistors in Parallel

31
Electric current and direct-current circuits The equivalent resistance for resistors in parallel is calculated by adding the reciprocal values of the individual resistors.

32
Electric current and direct-current circuits This gives the reciprocal of the equivalent resistance

33
Electric current and direct-current circuits For the example given

34
Electric current and direct-current circuits The current going through individual resistors connected in parallel is not necessarily the same.

35
Electric current and direct-current circuits The sum of the currents will be equal to the current calculated for the individual resistors.

36
Electric current and direct-current circuits For circuits that contain resistors connected both in series and in parallel, we first calculate the equivalent resistances.

37
Electric current and direct-current circuits We then treat the result as if it were just another resistor in series. Ex.21-7 on page 693.

38
Example 21-7 Combination Special

39
Electric current and direct-current circuits The sum of the voltage drops in a circuit must be equal to the voltage applied to the circuit.

40
Figure 21-16 Capacitors in Parallel

41
Electric current and direct-current circuits The equivalent capacitance for capacitors in parallel is just the sum of the individual capacitances

42
Electric current and direct-current circuits For the example given

43
Electric current and direct-current circuits The sum of the individual charges on the capacitors is equal to the charge on the equivalent capacitor.

44
Figure 21-17 Capacitors in Series

45
Electric current and direct-current circuits The equivalent resistance for capacitors in series is calculated by adding the reciprocal values of the individual capacitors.

46
Electric current and direct-current circuits This gives the reciprocal of the equivalent capacitance.

47
Electric current and direct-current circuits For the example given

48
Electric current and direct-current circuits Active example 21-3 p 700.

49
Electric current and direct-current circuits Kirchoff’s rules 1. The sum of the currents entering a junction, must equal the sum of the currents leaving that junction (result of charge conservation).

50
Electric current and direct-current circuits Kirchoff’s rules 2. The algebraic sum of the potential differences around a closed loop is zero. The potential increases in going from the negative to the positive terminal of a battery, and decreases when crossing a resistor in the direction of the current. (energy conservation).

51
Electric current and direct-current circuits Batteries – all non-ideal batteries have an internal resistance. The voltage measured across the terminals of a battery will be less with current flowing than without current flowing.

52
Electric current and direct-current circuits Ammeters are connected in series with the part of the circuit being tested. The ideal resistance of an ammeter is 0

53
Electric current and direct-current circuits Voltmeters are connected in series with the part of the circuit being tested. The ideal resistance of a voltmeter is ∞

Similar presentations

© 2021 SlidePlayer.com Inc.

All rights reserved.

To make this website work, we log user data and share it with processors. To use this website, you must agree to our Privacy Policy, including cookie policy.

Ads by Google