What does ESL mean?

ESL (English as a Second Language) is the general term for any course that teaches English. Whether in an English-speaking country or a non-English speaking country, it can be said to be an ESL course. In Europe and the United States, ESL courses are very common and are aimed at new immigrants and new international students, or for some foreign scholars who come here specifically to study. ESL (English as a Second Language) is a non-native English tutorial, which stands for English as a Second Language. ESL courses are taught in levels, generally ranging from levels A to E. Level A is the lowest level and level E is the highest level. The teaching project is a teaching project jointly developed by Royal Bridge Education Group of Canada and the Abbotsford School Board of Canada. Canada uses two official languages, so international students can come to Canada to study English as a Second Language (ESL) or French as a Second Language (FSL). ESL English is a required language course for international students entering North American universities. It is a world-recognized language course. ESL provides students with the opportunity to learn English in a communicative way. Many people choose to study English as a second language in Canada because of the many excellent English language schools in Canada. Because a large number of new immigrants need to learn English, Canada has trained a considerable number of professional ESL teachers over the years. At language schools, international students can study General English, Business English or English for Specific Purposes. Sometimes a single elective English course costs more than 1,000 Canadian dollars in tuition. Almost all universities and community colleges offer ESL courses. The ESL English course is based on the Canadian public school syllabus, allowing students whose native language is not English to reach the same level as Canadian high school students in English listening, speaking, reading and writing, allowing students from non-English speaking countries to quickly integrate with North American university courses, ESL student classes Divided into four levels and 12 levels, students take a test to determine their English proficiency before enrolling, and then choose a class that suits their level. Students at all levels take exams at the end of each period of study and are promoted to the next level after meeting the standards. And obtain an internationally recognized certificate of conformity at this level. So generally speaking, most ESL schools have flexible admission requirements and admission dates. Currently, North American countries require compulsory ESL courses for new immigrants from Eastern Europe, South America, India, China and other places whose native language is not English. ESL is not a required course. If you have TOEFL and IELTS scores, the TOEFL is basically 90-100 or above, and the IELTS is 6.5 or above, at least there is no need to take ESL in Canada. Or ESL (Equivalent Series Inductance) is the equivalent inductance parameter and ESR (equivalent resistance) is the two parameters of the capacitor. A capacitor will produce various impedances and inductive reactances due to its structure. The more important thing is the ESR equivalent series connection. Resistance and ESL Equivalent Series Inductance - This is the basis of capacitive reactance. Capacitors provide capacitance, why do we need resistors? Therefore, ESR and ESL are also required to be low...low; but low ESR/low ESL are usually high-end series. The level of ESR is related to the capacity, voltage, frequency and temperature of the capacitor. When the rated voltage is fixed, the larger the capacity, the lower the ESR. Some people are used to connecting multiple small capacitors in parallel to form a large capacitor to reduce impedance. The theory is that the resistance of resistors in parallel is reduced. However, if we consider the impedance of the solder joints of the capacitor pins, we may not necessarily gain anything from the small to the large. On the other hand, when the capacity is fixed, choosing a product with a high WV rated voltage can also reduce the ESR; therefore, there are indeed many benefits to having a high withstand voltage. Influence of frequency: ESR is high at low frequencies and low at high frequencies; of course, high temperatures will also cause an increase in ESR. The unit of equivalent series resistance ESR is mΩ, and advanced series capacitors are often low ESR and low ESL. If we compare the two characteristics of low internal resistance and low leakage current, low internal resistance is easy to achieve, so capacitors marked with low ESR are very common. ESR is related to the loss angle, ESR=tanδ/(ω×Cs), Cs is the capacitance. Sometimes there is Z on the capacitor specifications, which has a different meaning from ESR, but the calculation of Z is related to ESR, and also takes into account capacitive reactance and inductive reactance, which is the real internal resistance. I just mentioned that the ESR unit of a capacitor is mΩ, which refers to a large capacitor. If it is a 220μF small-capacity capacitor, its ESR unit is not mΩ but Ω. Early rolled capacitors often had very high ESL, and the larger the capacitance, the larger the ESL. ESL often becomes part of ESR, and ESL can also cause some circuit faults, such as series resonance. However, relative to the capacity, the proportion of ESL is too small, and the probability of problems is very small. Coupled with the advancement of capacitor manufacturing technology, ESL has been gradually ignored, and ESR is used as the main reference factor besides capacity.

By the way, capacitors also have a quality coefficient Q similar to that of inductors. This coefficient is inversely proportional to ESR and related to frequency, so it is rarely used.