WEBVTT 00:00.400 --> 00:07.240 All electrical circuits have three fundamental electromagnetic properties which are spread throughout 00:07.240 --> 00:08.720 the entire circuit. 00:09.320 --> 00:10.480 First, we have resistance. 00:10.480 --> 00:15.400 Here, resistance impedes the flow of electric current. 00:15.520 --> 00:21.200 In simpler words, it makes it harder for current to move through a material. 00:21.920 --> 00:27.800 As a result, electrical energy is not lost but transformed into heat. 00:28.160 --> 00:35.480 Now, this is why devices like light bulbs or phone chargers often feel warm during use. 00:36.160 --> 00:38.200 And we have the capacitance. 00:38.880 --> 00:45.240 Capacitance stores energy in an electrical field between two conductors. 00:45.840 --> 00:52.480 A key characteristics of a capacitor is that the voltage across it cannot change instantly. 00:52.960 --> 00:56.440 Now think of it like filling a bucket with water. 00:56.440 --> 00:58.200 You can't fill it immediately. 00:58.400 --> 01:02.880 It takes some time and we have the inductance here. 01:03.200 --> 01:10.080 Inductance stores energy in a magnetic field when current flows through a coil or a wire. 01:10.400 --> 01:17.040 Here the important point is that the current through an inductor cannot change instantly. 01:17.120 --> 01:23.120 So you can imagine like pushing a heavy object, it resists certain changes in moment. 01:23.760 --> 01:30.680 Now, because it takes time to build up an electrical field in a capacitor, capacitance slows down 01:30.840 --> 01:32.360 changes in voltage. 01:32.520 --> 01:36.320 Now similarly, it takes time to build up a magnetic field in an inductor. 01:36.320 --> 01:40.640 So inductance slows down changes in current. 01:40.920 --> 01:49.440 Now these two time dependent behaviors, along with resistance, together form what we call impedance. 01:49.880 --> 01:58.240 Impedance simply means resistance to change, whether it's a change in voltage or a current in a computer 01:58.330 --> 01:59.010 circuit. 01:59.050 --> 02:04.090 This impendence slows down the fast switching of electrical signals. 02:04.410 --> 02:10.250 Meanwhile, the pure resistance consumes electrical power by turning it into heat. 02:10.970 --> 02:17.530 In this lecture, we will mainly focus on the general timing characteristics of a resistance, capacitance 02:17.530 --> 02:18.810 and inductance. 02:19.290 --> 02:24.810 Discussions about power consumptions will be saved for more advanced lectures. 02:25.450 --> 02:30.490 Now, to better understand the real world effects of these properties, we will now look at the discrete 02:30.490 --> 02:36.970 electronic devices that are designed to introduce these properties at specific locations in a circuit. 02:37.450 --> 02:49.410 Now these devices are the resistors for resistance, capacitors for capacitors, and inductors for inductance. 02:50.170 --> 02:54.890 They all belong to a broader category called passive components. 02:54.930 --> 03:01.690 Now passive components are part of Circuit that cannot be actively controlled electronically. 03:01.690 --> 03:07.930 Instead, they simply store or consume energy without adding any external energy or making decisions. 03:08.650 --> 03:14.330 Now here you can see the standard circuit symbols for the passive devices we will discuss, which is 03:14.330 --> 03:14.890 switch. 03:15.570 --> 03:23.410 A switch simply opens or closes a circuit, not turning the current flow on or off 1 or 0. 03:24.090 --> 03:25.530 We have the resistor here. 03:26.050 --> 03:27.170 This is a resistor. 03:27.170 --> 03:29.810 Limits the current flow and produces heat. 03:30.530 --> 03:39.930 Capacitor A capacitor stores energy in an electric field and resists certain voltage changes, and inductor 03:40.370 --> 03:46.130 stores energy in a magnetic field and resists certain current changes. 03:46.850 --> 03:50.130 A switch can be in one of the two positions. 03:50.130 --> 03:54.330 It is either open or closed. 03:54.930 --> 04:00.460 In the open position, there is no connection between the two ends of the switch like this one. 04:01.220 --> 04:04.500 And therefore no electrical conduction occurs. 04:04.940 --> 04:08.340 No current can flow through the circuit, but. 04:08.380 --> 04:17.500 In a closed position, the connection between the two ends are complete, allowing the electricity to 04:17.540 --> 04:21.580 flow freely throughout the switch and the rest of the circuit. 04:22.220 --> 04:27.420 Now this symbol you can see here typically represent a manually activated switch. 04:27.580 --> 04:32.340 This means it is operated by a human hand, like flipping a light switch on a wall. 04:32.860 --> 04:39.780 And in the upcoming lectures titled transistors, you will learn that the computer uses transistors 04:39.780 --> 04:41.340 instead of manual switches. 04:41.580 --> 04:49.100 Now, these transistors act as electronic switches that can open or close automatically without human 04:49.100 --> 04:49.860 interaction. 04:50.300 --> 04:56.460 Now, by controlling these electronic switches, computers can implement on off logic, which is fundamental 04:56.500 --> 04:59.740 building blocks of all digital operations inside a computer. 05:00.540 --> 05:05.900 A resistor is used to limit the amount of current in a specific location within a circuit. 05:06.340 --> 05:13.740 By restricting the current flowing into a capacitor or an inductor, a resistor influences how long 05:13.740 --> 05:21.540 it takes for these other devices like capacitors and inductors, which will be discussed in detail later 05:21.820 --> 05:22.980 to store energy. 05:23.660 --> 05:31.300 The amount of resistance is usually carefully chosen, together with the amount of capacitance or inductance, 05:31.300 --> 05:34.820 to create specific timing characteristics in the circuit. 05:35.500 --> 05:42.180 Resistors are also used to limit the current flowing through sensitive devices, ensuring that the current 05:42.340 --> 05:50.900 stays at safe, non-destructive levels as a resistor limits current, it irreversibly transforms the 05:50.900 --> 05:59.550 electrical energy into heat, unlike capacitors or inductors and resistors, does not store energy. 05:59.550 --> 06:04.270 They simply convert it into heat without returning it to the circuit later. 06:04.990 --> 06:13.510 The relationship between voltage and the current for a single resistor is given by Ohm's Law V. 06:13.550 --> 06:23.310 Here is the voltage difference across a transistor at time T is time here I t. 06:23.350 --> 06:27.990 Here is the current flowing through it at the t time. 06:28.870 --> 06:36.910 R is the resistance of a value of the resistor, so the resistor values are specified in ohms. 06:37.790 --> 06:38.910 The symbol is this. 06:39.630 --> 06:46.350 Now the circuit I draw here illustrates two resistors connected through a switch to a power supply, 06:46.910 --> 06:49.390 which delivers five volts. 06:50.150 --> 06:55.750 The Greek letter ohm stands for ohms and kilo. 06:56.590 --> 07:01.390 Ohm means thousands ohms. 07:02.190 --> 07:04.470 No thousand ohms. 07:05.270 --> 07:12.270 Now, since current flows only in a closed path, no current flows until the switch is closed. 07:12.950 --> 07:20.150 Now in this diagram you can see five volt power supply provides a constant voltage of five volts to 07:20.150 --> 07:20.870 the circuit. 07:20.870 --> 07:30.630 Once the switch is closed and we have the switch here initially open, meaning no current flows. 07:31.430 --> 07:36.310 Now when the switch is closed, it completes the circuit, allowing the current to flow from the positive 07:36.350 --> 07:41.750 terminal of the battery through the resistors and back to the negative terminal. 07:42.550 --> 07:50.910 We have the resistors here, uh, one kilo ohms and 1.5 kilo ohms. 07:51.590 --> 07:57.070 These two resistors are connected in series, meaning the same current. 07:57.230 --> 08:03.790 In this case, I passes through both resistors one after another. 08:04.150 --> 08:10.070 In series circuit resistance adds together to form the total resistance. 08:10.870 --> 08:20.310 Now the arrow labeled here I shows the direction of the current flow from the positive terminal of the 08:20.310 --> 08:22.830 battery through the throat switch. 08:22.870 --> 08:29.510 Then the true through resistor and finally back to negative terminal. 08:30.230 --> 08:38.550 Now, because the resistors are in series, the five volts from the power supply is divided across the 08:38.550 --> 08:41.470 two resistors based on their resistance values. 08:42.190 --> 08:56.640 Now across 1.0 kilo ohms which is 1000Ω resistor which is between A and B, the voltage drop is 2.0V 08:57.480 --> 09:04.200 across the 1.5 kilo ohms, which is 1500Ω resistor. 09:04.440 --> 09:15.000 Between B and C, the voltage drop is 3.0V. 09:15.840 --> 09:32.280 The sum of these voltage drops, which is two or actually this 2.0V plus 3.0V equals to the total supplied 09:32.560 --> 09:38.960 voltage 5.0V satisfying the Kirchhoff's voltage law. 09:39.440 --> 09:48.520 So we have points A, B and C point A is where the current enters the first resistor. 09:48.800 --> 09:57.920 Point B is the junction between the two resistors, and point C is the end of the second resistor returning 09:57.960 --> 10:00.920 to the power source after the point C. 10:01.760 --> 10:09.600 Now in series connections, current is the same through all components, but the voltage divides according 10:09.640 --> 10:10.600 to resistance. 10:10.760 --> 10:16.240 Now the higher the resistance, the higher the voltage drop across that resistor. 10:16.960 --> 10:20.720 Now no current flows when the switch is open like this. 10:20.720 --> 10:22.640 But we make it like this. 10:22.960 --> 10:27.400 Then this is constantly flowing like that, right? 10:28.080 --> 10:35.360 And in this circuit here we have five volt power supply which supplies a constant five volts to the 10:35.360 --> 10:35.680 circuit. 10:35.680 --> 10:37.440 When the switch is closed. 10:38.160 --> 10:39.280 Right now it is open. 10:40.000 --> 10:43.640 When the switch is closed it completes the circuit allowing the current to flow. 10:43.960 --> 10:46.240 We have the two resistors here again. 10:47.200 --> 10:49.770 Now what is different than previous one. 10:49.810 --> 10:56.810 Right now that's because we have arranged them in a parallel connection, meaning they are connected 10:57.050 --> 11:07.250 side by side across the same points, which is A and C and voltage across resistors in parallel circuit. 11:07.490 --> 11:11.890 Each resistor experiences the fully supply voltage. 11:12.130 --> 11:12.690 Here. 11:12.890 --> 11:23.490 The both resistors here have the same five volts, five volts here again across them. 11:24.050 --> 11:30.090 And we have the current current I2 and current I, i1 and i2. 11:30.370 --> 11:43.890 This is the total current I t splits into two paths at the point a i1 flows through this one kilo ohm 11:43.890 --> 11:51.330 resistor, but I2 here flows through this 1.5 kilo ohm resistor. 11:52.090 --> 12:01.690 Now, using Ohm's law, we calculate the current through 1000 ohm resistor, which is I1 is equal to 12:02.570 --> 12:10.210 5.0mA and current through 1.5 kilo ohm resistor is 12:12.090 --> 12:25.890 3.3 milli ampere, and the total current supplied by the source is 8.38.3 milli amperes. 12:26.690 --> 12:29.050 And yeah, that was pretty easy right? 12:29.970 --> 12:38.570 Now in parallel connections, the voltage remains the same across all branches, but the current divides 12:38.610 --> 12:42.610 based on the resistance of each circuit. 12:44.730 --> 12:52.860 The branch with lower resistance allows more current to flow, while the branch with higher resistance, 12:52.860 --> 12:59.660 in this case 1.5 kilo ohms, allows less current to flow. 12:59.700 --> 13:04.500 Here the behavior follows Ohm's law. 13:04.940 --> 13:12.100 When resistance decreases, current increases for a given constant voltage and for the power distribution 13:12.100 --> 13:12.700 side. 13:12.740 --> 13:20.140 Each branch consists, consumes electrical power independently, and the total power consumed is the 13:20.180 --> 13:23.100 sum of the power across all branches. 13:23.900 --> 13:34.500 Now, in parallel circuits, voltage is constant across all paths, but current splits based on resistance. 13:35.220 --> 13:45.940 Lower resistance branches draw more current and the higher resistance branches draw less current.