13/2/2019 1 SELAMAT DATANG ASAS ELEKTRIK (BE001) BASIC ELECTRIC 1
13/2/2019 3 Academy KTM BASIC ELECTRIC MODULE 1 OVERVIEW OF BASIC ELECTRIC Electricity Ohm’s Law MODULE 2 PASSIVE ELEMENT Resistor Capasitor Switch Transformer Relay
13/2/2019 4 Academy KTM MODULE 3 ACTIVE ELEMENT Diode Transistor Bipolar Junction Transistor (BJT) Insulated-Gate Bipolar Transistor (IGBT) Integrated Circuit (IC) MODULE 4 GENERATOR / ALTERNATOR AC Power Supply DC Power Supply MODULE 5 Motor
13/2/2019 5 Academy KTM MODULE 6 ELECTROMAGNET Relay Contactor MODULE 7 ELECTRICITY APLICATION TO ROLLING STOCK Diesel Electric Transmission Power Electric Train Transmission Power Power Supply Conversion Basic Propulsion
13/2/2019 6 Academy KTM OBJEKTIF / Objective DI AKHIR KURSUS PESERTA AKAN / BOLEH :- At the end of the course participants should be able to : - MEMAHAMI KONSEP ASAS ELEKTRIK DAN PENGHASILANNYA Understanding basic of Electricity concept and producing MEMAHAMI, MENGENAL PASTI KOMPONEN PASIF DAN AKTIF Understanding, identify common passive and active component MEMAHAMI, MENGENAL PASTI FUNGSI PENJANA ELEKTRIK Understanding, identify common Electricity function
13/2/2019 7 Academy KTM APA ITU ELEKTRIK? What is electricity? PENGENALAN / Introduction UNTUK MEMAHAMI ASAS ELEKTRIK, KITA PERLU BERMULA DENGAN PEMAHAMAN ATOM To understand the fundamental of electricity we need to begin by focusing on atom
13/2/2019 8 Academy KTM BLOK BINAAN ATOM Building block of Atom UNSUR ATOM/ Elements of Atom
13/2/2019 9 Academy KTM BAHAGIAN DARIPADA ATOM Parts of Atom NUKLEUS / Nucleus TERLETAK DITENGAH ATOM Located at the center of atom PROTON / Protons ZARAH BERCAS POSITIF DIDALAM NUKLEUS Positively charged particles inside nucleus NEUTRON / Neutrons ZARAH BERCAS NEUTRAL DIDALAM NUKLEUS Uncharged particles inside nucleus ELECTRON / Electrons ZARAH BERCAS NEGATIF BERKEDUDUKAN PADA LUAR ORBIT NUKLEUS Negatively charged particles that orbit nucleus
13/2/2019 10 Academy KTM ATOM TEMBAGA Copper Atom MODEL ATOM / Bohr Atom
13/2/2019 11 Academy KTM CONTOH : SECARA RINGKAS ATOM WAYAR TEMBAGA Example : simplified copper wire atom ARAH CAS Flowing charges
13/2/2019 12 Academy KTM PENGALIR Conductors ADALAH BAHAN YANG MENGANDUNGI BILANGAN BESAR ELEKTRON BEBAS Material that contain large number of free electron KURANG RINTANGAN UNTUK PENGALIRAN ARUS Low resistance to current flow BAHAN PENGALIR Conductivity BAHAN / Material PENGALIRAN / Conductivity PERAK / Silver TEMBAGA / Cooper EMAS / Gold ALUMINIUM TUNGSTEN BESI / Iron Nichrome TINGGI High RENDAH Low
13/2/2019 13 Academy KTM PENEBAT Insulator ADALAH BAHAN YANG MENGHALANG ALIRAN ELEKTRIK Prevent the flow of electricity STABIL DENGAN MENYERAP PERGERAKAN ELEKTRON Stabilized by absorbing valence electrons KERINTANGAN YANG TINGGI BAGI PENGALIRAN ARUS High resistance to current flow BAHAN PENEBAT Insulator BAHAN / Material KETEBATAN / Insulator MICA KACA / Glass Teflon KERTAS / Paper (paraffin) GETAH / Rubber MINYAK / Oils UDARA / Air TINGGI High RENDAH Low
13/2/2019 14 Academy KTM KEGUNAAN BAHAN PENGALIR & PENEBAT The use of Conductive and Insulating materials
13/2/2019 15 Academy KTM SEPARA PENGALIR Semiconductor BOLEH DIUBAH UNTUK BERFUNGSI SAMA ADA SEBAGAI PENGALIR ATAU PENEBAT Can be altered to function as either a conductor or insulator ION NEGATIF – ION BERCAS NEGATIF Negative Ion - A negatively charged ion ION POSITIF – ION BERCAS POSITIF Positive Ion - A positively charged ion PENGIONAN – PROSES PENIGKATAN ATAU KEHILANGAN ELEKTRON – KETARAAN PENGALIRAN ARUS Ionization – The process of gaining or losing electron – Significant in current flow BAHAN SEPARA PENGALIR Semiconductor
13/2/2019 16 Academy KTM ELEKTRIK IALAH PENGALIRAN CAS MELALUI PUSINGAN LITAR YANG MEMBAWA TENAGA DARI BATERI (ATAU BEKALAN KUASA) KEPADA ALATAN SEPERTI LAMPU DAN MOTOR Electricity is the flow of charge around a circuit carrying energy from the battery (or power supply) to components such as lamps and motors. TENAGA ELEKTRIK HANYA BOLEH MENGALIR PADA LITAR YANG LENGKAP, DARI BATERI MELALUI WAYAR (PENGALIR) TERUS KE KOMPONEN DAN BALIK KE BATERI SEMULA Electricity can flow only if there is a complete circuit from the battery through wires to components and back to the battery again ELEKTRIK Electricity TENAGA ELEKTRIK Electricity
13/2/2019 17 Academy KTM CAS ELEKTRIK Electrical Charge ELEKTRIK ADALAH GERAKAN OLEH ELEKTRON Electricity is the movement of electrons ELEKTRON MENGHASILKAN CAS, YANG KITA BOLEH MEMANFAATKAN UNTUK MELAKUKAN KERJA Electrons create charge, which we can harness to do work ELEKTRIK Electricity CARA PENGECASAN Methods Of Charging PENGECASAN MELALUI GESERAN Charging By Friction PENGECASAN MELALUI ARUHAN Charging By Induction PENGECASAN MELALUI PENGALIRAN Charging By Conduction
13/2/2019 18 Academy KTM CIRI YANG ADA DALAM ELEKTRIK Characteristic Of Electricity and Current Flow VOLTAN Voltage ARUS Current RINTAGAN Resistance Key Terms: Charge = Strength (KEKUATAN) Current = Rate of Flow (KADAR ALIRAN) Voltage = Driving Force / Potential Difference (PENGGERAK / BEZA UPAYA) Resistance or Impendence = opposition (TENTANGAN) ELEKTRIK Electricity
13/2/2019 19 Academy KTM PERSAMAAN KONSEP VOLTAN Analogy of Voltage Menentukan Voltan sebagai jumlah Tenaga keupayaan antara dua titik didalam sesuatu litar (Tekanan = Voltan) We define voltage as the amount of potential energy between two points on a circuit (Pressure = Voltage) DIUKUR PADA UNIT VOLT Measured in Volt ELEKTRIK Electricity A B
13/2/2019 20 Academy KTM PERSAMAAN KONSEP VOLTAN Analogy of Voltage ELEKTRIK Electricity TIDAK DIBEKALKAN PUMP / TEKANAN No Supply of Pressure DIBEKALKAN PUMP / TEKANAN Supply of Pressure / Pump TIDAK DIBEKALKAN VOLTAN No Supply of Voltage DIBEKALKAN VOLTAN Supply of Voltage
13/2/2019 21 Academy KTM JENIS BEZA UPAYA (VOLTAN) Type of Potential Difference (Voltage) ELEKTRIK Electricity ARUS ULANG ALIK / Alternating Current (AC) ARUS TERUS/ Direct Current (DC)
13/2/2019 22 Academy KTM JENIS BEZA UPAYA (VOLTAN) Type of Potential Difference (Voltage) ELEKTRIK Electricity ANALOGI Analogy
13/2/2019 23 Academy KTM PERSAMAAN KONSEP ARUS Analogy of Current ARUS IALAH ALIRAN CAS ELEKTRIK (KUANTITI ALIRAN AIR = ARUS) Current is a flow of Electrical charge carriers (Quantity Flow of Water = Current) BERKADAR TERUS DENGAN VOLTAN, BERKURANG DENGAN NILAI KERINTANGAN Current is directly Proportional to Voltage, current less with Resistance DALAM CONVENTIONAL CURRENT ATAU FRANKLIN CURRENT, ALIRAN DARI POSITIF KE NEGATIF In conventional current or “Franklin current”, the flow from positive to negative points DALAM ELEKTRON, CAS DIBAWA NEGATIF, ALIRAN DARI NEGATIF KE POSITIF In electron, the most common charge carriers, are negative charged. They flow from negative to positive points PENGGUNAAN ARUS ELETRIK SAMA ADA “TERUS” ATAU “ULANG ALIK” Electric current can be either direct or alternating DIUKUR PADA UNIT AMPERE Measured in Ampere ELEKTRIK Electricity A B
13/2/2019 24 Academy KTM PERSAMAAN KONSEP RINTANGAN Analogy of Resistance PENENTANGAN / HADKAN ALIRAN ARUS ELEKTRIK Opposition / limitation to the flow of Electric charge DIUKUR PADA UNIT OHM (Ω) Measured in Ohm (Ω) ELEKTRIK Electricity
13/2/2019 25 Academy KTM DIFINASI KOMPONEN PASIF & AKTIF Definition of Passive & Active Component PENGENALAN KEPADA KOMPONEN ELEKTRONIK Introduction of Electronic Components KOMPONEN PASIF MERUPAKAN KOMPONEN ELEKTRONIK YANG TIDAK MEMERLUKAN ARUS ELEKTRIK UNTUK BEKERJA ATAU DIAKTIFKAN, KOMPONEN PASIF TIDAK BERSIFAT UNTUK MENGUATKAN, MENYEARAHKAN DAN MENGUBAH SATU BENTUK TENAGA KE BENTUK TENAGA LAIN Passive Components no need Electricity to activate, not able to amplifies, not to Current pass in one direction, and not transform energy to other KOMPONEN AKTIF MERUPAKAN KOMPONEN YANG MEMERLUKAN ARUS ELEKTRIK UNTUK BEKERJA ATAU DIAKTIFKAN Active Component must to supply electricity to activate the functioning of components
13/2/2019 26 Academy KTM JENIS KOMPONEN ELEKTRONIK Types of Electronic Components PENGENALAN KEPADA KOMPONEN ELEKTRONIK Introduction of Electronic Components Passive Elements Active Elements Resistor Diode Capacitor Transistor Inductor Integrated Circuit (IC) Switch Relay Transformer Transducer
13/2/2019 27 Academy KTM JENIS KOMPONEN ELEKTRONIK Types of Electronic Components PASSIVE ELEMENT
13/2/2019 28 Academy KTM PERINTANG Resistor JENIS KOMPONEN ELEKTRONIK Types of Electronic Components KEGUNAAN PERINTANG DALAM LITAR ADALAH UNTUK MENGAWAL ALIRAN ARUS PADA KOMPONEN LAIN / MENGHADKAN PENGALIRAN ARUS The main function of Resistor in a circuit to control flow of current to other components. So a Resistor is used to limit the current UNIT SUKATAN OHM (Ω) Measured in Ohm (Ω)
13/2/2019 29 Academy KTM PERINTANG TETAP & SIMBOL Fixed Resistor & Symbols JENIS KOMPONEN ELEKTRONIK Types of Electronic Components NILAI KERINTANGAN TIDAK BOLEH DIUBAH Resistance value does not change TERDIRI DARIPADA DUA TERMINAL Consists of two terminals IEC Symbols (New) International Electrotechnical Commission IEEE Symbols (Old) Institute of Electrical and Electronics Engineers
13/2/2019 30 Academy KTM PERINTANG BOLEH UBAH & SIMBOL Variable Resistor & Symbol JENIS KOMPONEN ELEKTRONIK Types of Electronic Components NILAI KERINTANGAN BOLEH DIUBAH Adjustable value Resistance PERINTANG DIKAWAL BERKURANG ATAU BERTAMBAH NILAI KERINTANGAN BAGI ALIRAN ELEKTRIK YANG SESUAI A Resistor that controls (increase or decrease) the flow of electric current when we change its resistance IEC Symbols (New) International Electrotechnical Commission IEEE Symbols (Old) Institute of Electrical and Electronics Engineers
13/2/2019 31 Academy KTM JENIS - JENIS PERINTANG Types of Resistor JENIS KOMPONEN ELEKTRONIK Types of Electronic Components Fixed Resistor Variable Resistor Carbon Composite Resistor Potentiometer Carbon Film Resistor Rheostat Wire Wound Resistor Thermistor Chip Resistor Photoresistor (LDR)
13/2/2019 32 Academy KTM JENIS - JENIS PERINTANG Types of Resistor JENIS KOMPONEN ELEKTRONIK Types of Electronic Components Carbon Composite Resistor IA DIPERBUAT DARIPADA ZARAH KARBON YANG TERBAIK, DIADUN DENGAN BAHAN RINTANGAN ; GRAFIT, DEBUAN SERAMIK DAN RESIN They are made out of fine carbon particles mixed with resistive material ; graphite, ceramic dust and resin. KELEBIHAN (Advantages) KEKURANGAN (Disadvantages) KEUPAYAAN UNTUK MENAHAN DENYUTAN TENAGA YANG TINGGI Ability to withstand high energy pulses KOS BINAA MURAH Cheap to make KURANG STABIL (RINTANGAN DARI BINAAN KOMPOSIT KARBON AKAN BERUBAH DENGAN CEPAT Poor stability (resistance of carbon composition resistor will change rapidly) KETEPATAN YANG RENDAH Low accuracy KEGUNAAN / Application MELINDUNGI LITAR (LONJAKAN ATAU NYAHCAS), HADKAN ARUS, BEKALAN KUASA TINGGI, WELDING Protection of circuit (Surge @ Discharge protection), current limiting,high voltage power supply, welding
13/2/2019 33 Academy KTM JENIS - JENIS PERINTANG Types of Resistor JENIS KOMPONEN ELEKTRONIK Types of Electronic Components Carbon Film Resistor DIBUAT DENGAN LAPISAN YANG SANGAT NIPIS DARI KARBON PADA ROD SERAMIK Made by depositing a very thin layer of carbon on a ceramic rod DILINDUNGI OLEH JAKET KEBAKARAN (IA AKAN MEMBAKAR JIKA BEBAN LAMPAU MENCUKUPI) Protected by a flameproof jacket (it will burn if overloaded sufficiently) MENGURANGKAN GANGUAN ELEKTRIK BERBANDING KOMPOSIT KARBON Produce less electrical noise than carbon composite KEGUNAAN / Application BEKALAN KUASA TINGGI DAN SUHU TINGGI, High voltage power supply and temperature
13/2/2019 34 Academy KTM NILAI PERINTANG Value of Resistor JENIS KOMPONEN ELEKTRONIK Types of Electronic Components
13/2/2019 35 Academy KTM JENIS - JENIS PERINTANG Types of Resistor JENIS KOMPONEN ELEKTRONIK Types of Electronic Components Wire Wound Resistor DIPERBUAT DARIPADA TERAS ATAU ROD PENEBAT DENGAN DIBALUTI SEKELILINGNYA DAWAI RINTANGAN Made from the insulating core or rod by wrapping around a resistive wire DAWAI RINTANGAN BIASANYA TUNGSTEN, MANGANIN, NIKROM ATAU NIKEL ATAU NIKEL ALOI KROMIUM DAN TERAS PENEBAT DIPERBUAT DARIPADA PORSELIN, BAKELITE, KERTAS, ATAU BAHAN TANAH LIAT SERAMIK The resistance wire is generally tungsten, manganin, nichrome or nickel or nickel chromium alloy and the insulating core is made of porcelain, bakelite, press bond paper or ceramic clay material KEGUNAAN / Application BEKALAN KUASA TINGGI DAN SENSETIF TINGGI,KETEPATAN DAN PENGAWALAN KESEIMBANGAN ARUS ELEKTRIK DI DALAM KAWALAN PERALATAN INDUSTRI High voltage power supply and high sensititvity, accurate and balanced current control, Generally used in high power rating devices and equipments, Industrial.
13/2/2019 36 Academy KTM JENIS - JENIS PERINTANG Types of Resistor JENIS KOMPONEN ELEKTRONIK Types of Electronic Components Chip Resistor CIRI – CIRI KECIL, CHIP RESISTOR SELALUNYA BERBENTUK SEGI EMPAT TEPAT DENGAN PANJANG DAN LEBAR PERANTI MENETUKAN NILAINYA Characteristics, Small, chip resistor almost always square or rectangular, with the length and width of the device determining their power ratings CHIP RESISTOR JENIS SMD Chip resistor are typically surface mount device (SMD) IA DIPASANG TERUS PADA PAPAN LITAR TERCETAK (PCB) They are mounted directly onto a printed circuit board (PCB) KEGUNAAN / Application PERANTI ELEKTRONIK, ALAT TELEKOMUNIKASI, ALAT ELEKTRONIK PERUBATAN, ALAT KAWALAN, KOMPUTER Electronic device, Telecommunication device, Medical equipment, automatic equipment controller, Computer
13/2/2019 37 Academy KTM NILAI PERINTANG Value of Resistor JENIS KOMPONEN ELEKTRONIK Types of Electronic Components 47KΩ
13/2/2019 38 Academy KTM NILAI PERINTANG Value of Resistor JENIS KOMPONEN ELEKTRONIK Types of Electronic Components
13/2/2019 39 Academy KTM JENIS - JENIS PERINTANG Types of Resistor JENIS KOMPONEN ELEKTRONIK Types of Electronic Components Potentiometer ANTARA KEDUA-DUA PIN SISI POTENTIOMETER TERDAPAT JALUR BAHAN RINTANGAN. CONTOHNYA SEPERTI KARBON. BAHAN INI MEWUJUDKAN RINTANGAN Between the two side pins of the Potentiometer there is a strip of resistive material. For example as carbon. This material creates resistance. PERUBAHAN NILAI RINTANGAN BERLAKU BILA PUSINGAN SHAFT DILAKUKAN When you move the shaft / wiper, the resistance will be decrease or increases. KEGUNAAN / Application PERANTI ELEKTRONIK, MENGAWAL VOLUME ALATAN MUZIK, MENGAWAL KECERAHAN LAMPU DAN BANYAK LAGI KEGUNAAN LAIN Electronic device, such as to control the volume of music equipment, control the brightness of a light and much more.
13/2/2019 40 Academy KTM JENIS - JENIS PERINTANG Types of Resistor JENIS KOMPONEN ELEKTRONIK Types of Electronic Components Rheostat RHEOSTAT DIPERBUAT DARI LILITAN WAYAR / DAWAI NICHROM PADA PENEBAT TERAS SERAMIK. TERAS SERAMIK SEBAGAI BAHAN PENEBAT YANG MENGHALANG ALIRAN HABA Rheostats are made by winding the Nichrome wire around an insulating ceramic core. The ceramic core of the rheostat acts as the insulating material to the heat. Hence, the ceramic core does not allow heat through it PERUBAHAN NILAI RINTANGAN BERLAKU BILA WIPER DILAKUKAN PEMACUAN (MASUKAN TERMINAL “A” KELUARAN “B”) When you move the shaft / wiper, the resistance will be decrease or increases (Input terminal “A” Output terminal “B”). KEGUNAAN / Application MENGAWAL KECERAHAN LAMPU, KELAJUAN MOTOR To control the brightness of a light, speed of motor
13/2/2019 41 Academy KTM JENIS - JENIS PERINTANG Types of Resistor JENIS KOMPONEN ELEKTRONIK Types of Electronic Components Thermistor SEJENIS RINTANGAN HABA,NILAI RINTANGAN BERGANTUNG PADA SUHU, IA DIPERBUAT DARIPADA OKSIDA LOGAM,DIMAMPAT KEDALAM MANIK, BERBENTUK CAKERA ATAU SILINDER KEMUDIAN DIMUATKAN DENGAN BAHAN TELAP SEPERTI EPOXY ATAU KACA A thermistor is a resistance thermometer, or a resistor whose resistance is dependent on temperature. The term is a combination of "thermal" and “resistor” . It is made of metallic oxides, press into a bead, disk or cylindrical shape and then encapsulated with an impermeable material such as expoxy or glass
13/2/2019 42 Academy KTM JENIS - JENIS PERINTANG Types of Resistor JENIS KOMPONEN ELEKTRONIK Types of Electronic Components Thermistor JENIS THERMISTOR / Types of thermistor Negative Temperature Co-efficient (NTC) Thermistors – resistance increases when temperature decreases Positive Temperature Co-efficient (PTC) Thermistors - resistance increases when temperature increases KEGUNAAN / Application MENGAWAL SISTEM PEMANASAN AIR, SISTEM KEBAKARAN To control Water heating system, Fire alarm system NTC
13/2/2019 43 Academy KTM JENIS - JENIS PERINTANG Types of Resistor JENIS KOMPONEN ELEKTRONIK Types of Electronic Components Photo Resistor / LDR (Light Dependent Resistors) SEJENIS RINTANGAN PEKA CAHAYA,NILAI RINTANGAN BERGANTUNG PADA KECERAHAN CAHAYA, KECERAHAN CAHAYA MENURUNKAN NILAI RINTANGAN A Photoresistor are used in many applications because they either increase or decrease in resistance depending on the amount of light, resistance decrease when light increases KEGUNAAN / Application DIGUNAKAN PADA PELBAGAI ALAT SEPERTI PENGGERA, LAMPU SOLAR JALANAN, they are also used in various device such as alarm device, solar street lamps, night-light
13/2/2019 44 Academy KTM SAMBUNGAN LITAR PERINTANG Circuit of Resistor JENIS KOMPONEN ELEKTRONIK Types of Electronic Components SAMBUNGAN SIRI Series Circuit SAMBUNGAN SELARI Parallel Circuit
13/2/2019 45 Academy KTM KAPASITOR Capacitor JENIS KOMPONEN ELEKTRONIK Types of Electronic Components KOMPONEN YANG MENERIMA CAS DAN MELEPASKAN CAS ELEKTRIK The components that receive the charge and release the charge UNIT SUKATAN FARAD (F) Measured in Farad (F) KEGUNAAN / Application MENYIMPAN TENAGA / CAS DARI BEKALAN KUASA UNTUK SEMENTARA Store Electric Charge from power supply for temporarily MEMPERUNTUKAN PENAPIS FLEKSIBEL PADA BEKALAN KUASA Flexible Filter to power supply
13/2/2019 46 Academy KTM JENIS KOMPONEN ELEKTRONIK Types of Electronic Components KAPASITOR SERAMIK Ceramic Capacitor KAPASITOR ELEKTROLITIK Electrolytic Capacitor KAPASITOR POLYPROPYLENE (PP) FILEM Polypropylene (PP) Film Capacitor KAPASITOR MIKA Mica Capacitor JENIS - JENIS KAPASITOR Types of Capacitor
13/2/2019 47 Academy KTM JENIS KOMPONEN ELEKTRONIK Types of Electronic Components DIELECTRIC BOLEH DIPERBUAT MENGGUNAKAN KERTAS, PLASTIK, MIKA, CERAMIK, KACA, VACUUM ATAU JENIS BAHAN BUKAN PENGALIR Dielectric can be made of paper, plastic, mica, ceramic, glass, vacuum or any type of non-conductive material METAL PLATE DIBUAT DARI BAHAN PENGALIR SEPERTI ALUMINIUM, TANTALUM, PERAK, ATAU BAHAN LAIN. The plates are made of conductive material: aluminum, tantalum, silver, or other metals BAHAN BINAAN KAPASITOR Building Materials of Capacitor
13/2/2019 48 Academy KTM JENIS KOMPONEN ELEKTRONIK Types of Electronic Components SUMBER BEKALAN CAS ELEKTRIK DISIMPAN PADA METAL PLATE Power Supply Storage Electric Charges in Metal Plates CAS POSITIF DAN NEGATIF SALING MENARIK DI METAL PLATE The positive and negative charges on each of these plates attract each other BAGAIMANA KAPASITOR BEKERJA? How Capacitor Work?
13/2/2019 49 Academy KTM JENIS KOMPONEN ELEKTRONIK Types of Electronic Components DICAS DAN NYAHCAS Charging and Discharging BAGAIMANA KAPASITOR BEKERJA? How Capacitor Work?
13/2/2019 50 Academy KTM SAMBUNGAN LITAR KAPASITOR Circuit of Capacitor JENIS KOMPONEN ELEKTRONIK Types of Electronic Components SAMBUNGAN SIRI Series Circuit SAMBUNGAN SELARI Parallel Circuit